Rearrange positive and negative numbers with constant extra space

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Given an array of positive and negative numbers, arrange them such that all negative integers appear before all the positive integers in the array without using any additional data structure like a hash table, arrays, etc. The order of appearance should be maintained.

Examples:

Input:  [12 11 -13 -5 6 -7 5 -3 -6]
Output: [-13 -5 -7 -3 -6 12 11 6 5]

A simple solution is to use another array. We copy all elements of the original array to a new array. We then traverse the new array and copy all negative and positive elements back into the original array one by one. This approach is discussed. The problem with this approach is that it uses an auxiliary array and we’re not allowed to use any data structure to solve this problem.

One approach that does not use any data structure is to use the partition process of QuickSort. The idea is to consider 0 as a pivot and divide the array around it. The problem with this approach is that it changes the relative order of elements. A similar partition process is discussed here.
Let’s now discuss a few methods which do not use any other data structure and also preserve the relative order of elements.

Approach 1: Modified Partition Process of Quick Sort

We can reverse the order of positive numbers whenever the relative order is changed. This will happen if there are more than one positive element between the last negative number in the left subarray and the current negative element.

Below are the steps on how this will happen:

Current Array :- [Ln, P_1,P_2,P_3,N_1,.......]
Here, Ln is the left subarray(can be empty) that contains only negative elements. P₁, P_2,P₃ are the positive numbers and N₁
is the negative number that we want to move at correct place.
If difference of indices between positive number and negative number is greater than 1,
    1. Swap P₁ and N_1,we get [Ln, N₁, P₂, P₃, P₁, ......]
    2. Rotate array by one position to right, i.e. rotate array [P_2,P_3,P_1], we get [Ln, N₁, P₁, P₂, P₃, ......]

Below is the implementation for the same as follows:

C++

// C++ program to Rearrange positive and negative
// numbers in a array
#include <bits/stdc++.h>
using namespace std;
 
// A utility function to print an array of size n
void printArray(int arr[], int n)
{
    for (int i = 0; i < n; i++)
        cout<<arr[i]<<" ";
}
 
void rotateSubArray(int arr[], int l, int r) {
int temp = arr[r];
for (int j = r; j > l - 1; j--) {
  arr[j] = arr[j - 1];
}
arr[l] = temp;
}
  
void moveNegative(int arr[], int n) 
{
 
    int last_negative_index = -1;
     
    for (int i = 0; i < n; i++) {
      if (arr[i] < 0) {
        last_negative_index += 1;
        int temp = arr[i];
        arr[i] = arr[last_negative_index];
        arr[last_negative_index] = temp;
     
        // Done to manage order too
        if (i - last_negative_index >= 2)
          rotateSubArray(arr, last_negative_index + 1, i);
      }
}
}
  
// Driver Code
int main()
{
    int arr[] = { 5, 5, -3, 4, -8, 0, -7, 3, -9, -3, 9, -2, 1 };
    int n = sizeof(arr) / sizeof(arr[0]);
  
    moveNegative(arr, n);
    printArray(arr, n);
  
    return 0;
}
 
// This code is contributed by Aarti_Rathi

Java

// Java program for
// moving negative numbers to left
// while maintaining the order
import java.io.*;
class GFG {
 
    static int[] rotateSubArray(int[] arr, int l, int r)
    {
        int temp = arr[r];
        for (int j = r; j > l - 1; j--) {
            arr[j] = arr[j - 1];
        }
        arr[l] = temp;
 
        return arr;
    }
 
    static int[] moveNegative(int[] arr)
    {
 
        int last_negative_index = -1;
 
        for (int i = 0; i < arr.length; i++) {
            if (arr[i] < 0) {
                last_negative_index += 1;
                int temp = arr[i];
                arr[i] = arr[last_negative_index];
                arr[last_negative_index] = temp;
 
                // Done to manage order too
                if (i - last_negative_index >= 2)
                    rotateSubArray(
                        arr, last_negative_index + 1, i);
            }
        }
 
        return arr;
    }
 
    // Driver Code
    public static void main(String args[])
    {
        int[] arr = { 5, 5,  -3, 4, -8, 0, -7,
                      3, -9, -3, 9, -2, 1 };
        arr = moveNegative(arr);
 
        for (int i : arr) {
            System.out.print(i + " ");
        }
    }
}
// This code is contributed by Saurabh Jaiswal

Python3

# Python 3 program for
# moving negative numbers to left
# while maintaining the order
 
 
class Solution:
    def rotateSubArray(self, arr, l, r):
        temp = arr[r]
        for j in range(r, l-1, -1):
            arr[j] = arr[j-1]
        arr[l] = temp
 
        return arr
 
    def moveNegative(self, arr):
 
        last_negative_index = -1
 
        for i in range(len(arr)):
            if arr[i] < 0:
                last_negative_index += 1
                arr[i], arr[last_negative_index] = arr[last_negative_index], arr[i]
 
                # Done to manage order too
                if i - last_negative_index >= 2:
                    self.rotateSubArray(arr, last_negative_index+1, i)
 
        return arr
 
 
#  Driver Code
if __name__ == '__main__':
    arr = [5, 5, -3, 4, -8, 0, -7, 3, -9, -3, 9, -2, 1]
    ob = Solution()
    ob.moveNegative(arr)
    for i in arr:
        print(i, end=' ')
    print()
 
# This code is contributed by Kapil Bansal(devkapilbansal)

C#

// C# program for
// moving negative numbers to left
// while maintaining the order
using System;
class GFG {
 
  static int[] rotateSubArray(int[] arr, int l, int r) {
    int temp = arr[r];
    for (int j = r; j > l - 1; j--) {
      arr[j] = arr[j - 1];
    }
    arr[l] = temp;
 
    return arr;
  }
 
  static int[] moveNegative(int[] arr) {
 
    int last_negative_index = -1;
 
    for (int i = 0; i < arr.Length; i++) {
      if (arr[i] < 0) {
        last_negative_index += 1;
        int temp = arr[i];
        arr[i] = arr[last_negative_index];
        arr[last_negative_index] = temp;
 
        // Done to manage order too
        if (i - last_negative_index >= 2)
          rotateSubArray(arr, last_negative_index + 1, i);
      }
    }
 
    return arr;
  }
 
  // Driver Code
  public static void Main() {
    int[] arr = { 5, 5, -3, 4, -8, 0, -7, 3, -9, -3, 9, -2, 1 };
    arr = moveNegative(arr);
 
    foreach (int i in arr) {
      Console.Write(i + " ");
    }
  }
}
 
// This code is contributed by gfgking.

Javascript

<script>
 
// JavaScript program for
// moving negative numbers to left
// while maintaining the order
 
 
class Solution{
     
    rotateSubArray(arr, l, r){
        let temp = arr[r]
        for(let j = r;j > l-1;j--){
            arr[j] = arr[j-1]
        }
        arr[l] = temp
 
        return arr
    }
 
     
    moveNegative(arr){
 
        let last_negative_index = -1
 
        for(let i=0;i<arr.length;i++){
            if(arr[i] < 0){
                last_negative_index += 1
                let temp = arr[i];
                arr[i] = arr[last_negative_index];
                arr[last_negative_index] = temp;
 
                // Done to manage order too
                if(i - last_negative_index >= 2)
                    this.rotateSubArray(arr, last_negative_index+1, i)
            }
        }
 
        return arr
    }
}
 
 
//  Driver Code
 
let arr = [5, 5, -3, 4, -8, 0, -7, 3, -9, -3, 9, -2, 1]
let ob = new Solution()
ob.moveNegative(arr)
for(let i of arr){
    document.write(i,' ')
}
 
// This code is contributed by shinjanpatra
 
</script>

PHP

<?php
// A utility function to print an array of size n
function printArray($arr, $n) {
    for ($i = 0; $i < $n; $i++) {
        echo $arr[$i] . " ";
    }
}
 
function rotateSubArray(&$arr, $l, $r) {
    $temp = $arr[$r];
    for ($j = $r; $j > $l - 1; $j--) {
        $arr[$j] = $arr[$j - 1];
    }
    $arr[$l] = $temp;
}
 
function moveNegative(&$arr, $n) {
    $last_negative_index = -1;
    for ($i = 0; $i < $n; $i++) {
        if ($arr[$i] < 0) {
            $last_negative_index += 1;
            $temp = $arr[$i];
            $arr[$i] = $arr[$last_negative_index];
            $arr[$last_negative_index] = $temp;
 
            // Done to manage order too
            if ($i - $last_negative_index >= 2) {
                rotateSubArray($arr, $last_negative_index + 1, $i);
            }
        }
    }
}
 
$arr = array(5, 5, -3, 4, -8, 0, -7, 3, -9, -3, 9, -2, 1);
$n = sizeof($arr) / sizeof($arr[0]);
 
moveNegative($arr, $n);
printArray($arr, $n);
?>

Output

-3 -8 -7 -9 -3 -2 5 5 4 0 3 9 1

Time Complexity: O(n²)
Auxiliary Space: O(1)

Approach 2: Modified Insertion Sort

We can modify insertion sort to solve this problem.

Algorithm:

Loop from i = 1 to n - 1.
  a) If the current element is positive, do nothing.
  b) If the current element arr[i] is negative, we 
     insert it into sequence arr[0..i-1] such that 
     all positive elements in arr[0..i-1] are shifted 
     one position to their right and arr[i] is inserted
     at index of first positive element.

Below is the implementation –

C++

// C++ program to Rearrange positive and negative
// numbers in a array
#include <stdio.h>
 
// A utility function to print an array of size n
void printArray(int arr[], int n)
{
    for (int i = 0; i < n; i++)
        printf("%d ", arr[i]);
    printf("\n");
}
 
// Function to Rearrange positive and negative
// numbers in a array
void RearrangePosNeg(int arr[], int n)
{
    int key, j;
    for (int i = 1; i < n; i++) {
        key = arr[i];
 
        // if current element is positive
        // do nothing
        if (key > 0)
            continue;
 
        /* if current element is negative,
        shift positive elements of arr[0..i-1],
        to one position to their right */
        j = i - 1;
        while (j >= 0 && arr[j] > 0) {
            arr[j + 1] = arr[j];
            j = j - 1;
        }
 
        // Put negative element at its right position
        arr[j + 1] = key;
    }
}
 
/* Driver program to test above functions */
int main()
{
    int arr[] = { -12, 11, -13, -5, 6, -7, 5, -3, -6 };
    int n = sizeof(arr) / sizeof(arr[0]);
 
    RearrangePosNeg(arr, n);
    printArray(arr, n);
 
    return 0;
}

Java

// Java program to Rearrange positive
// and negative numbers in a array
import java.io.*;
 
class GFG {
    // A utility function to print
    // an array of size n
    static void printArray(int arr[], int n)
    {
        for (int i = 0; i < n; i++)
            System.out.print(arr[i] + " ");
        System.out.println();
    }
 
    // Function to Rearrange positive and negative
    // numbers in a array
    static void RearrangePosNeg(int arr[], int n)
    {
        int key, j;
        for (int i = 1; i < n; i++) {
            key = arr[i];
 
            // if current element is positive
            // do nothing
            if (key > 0)
                continue;
 
            /* if current element is negative,
            shift positive elements of arr[0..i-1],
            to one position to their right */
            j = i - 1;
            while (j >= 0 && arr[j] > 0) {
                arr[j + 1] = arr[j];
                j = j - 1;
            }
 
            // Put negative element at its right position
            arr[j + 1] = key;
        }
    }
 
    // Driver program
    public static void main(String[] args)
    {
        int arr[] = { -12, 11, -13, -5, 6, -7, 5, -3, -6 };
        int n = arr.length;
        RearrangePosNeg(arr, n);
        printArray(arr, n);
    }
}
 
// This code is contributed by vt_m.

Python 3

# Python 3 program to Rearrange positive
# and negative numbers in a array
 
# A utility function to print
# an array of size n
 
 
def printArray(arr, n):
    for i in range(n):
        print(arr[i], end=" ")
    print()
 
# Function to Rearrange positive
# and negative numbers in a array
 
 
def RearrangePosNeg(arr, n):
 
    for i in range(1, n):
        key = arr[i]
 
        # if current element is positive
        # do nothing
        if (key > 0):
            continue
 
        ''' if current element is negative,
        shift positive elements of arr[0..i-1],
        to one position to their right '''
        j = i - 1
        while (j >= 0 and arr[j] > 0):
            arr[j + 1] = arr[j]
            j = j - 1
 
        # Put negative element at its
        # right position
        arr[j + 1] = key
 
 
# Driver Code
if __name__ == "__main__":
    arr = [-12, 11, -13, -5,
           6, -7, 5, -3, -6]
    n = len(arr)
 
    RearrangePosNeg(arr, n)
    printArray(arr, n)
 
# This code is contributed
# by ChitraNayal

C#

// C# program to Rearrange positive
// and negative numbers in a array
using System;
 
class GFG {
 
    // A utility function to print
    // an array of size n
    static void printArray(int[] arr, int n)
    {
        for (int i = 0; i < n; i++)
            Console.Write(arr[i] + " ");
        Console.WriteLine();
    }
 
    // Function to Rearrange positive and negative
    // numbers in a array
    static void RearrangePosNeg(int[] arr, int n)
    {
        int key, j;
        for (int i = 1; i < n; i++) {
            key = arr[i];
 
            // if current element is positive
            // do nothing
            if (key > 0)
                continue;
 
            /* if current element is negative,
            shift positive elements of arr[0..i-1],
            to one position to their right */
            j = i - 1;
            while (j >= 0 && arr[j] > 0) {
                arr[j + 1] = arr[j];
                j = j - 1;
            }
 
            // Put negative element at its right position
            arr[j + 1] = key;
        }
    }
 
    // Driver program
    public static void Main()
    {
        int[] arr = { -12, 11, -13, -5, 6, -7, 5, -3, -6 };
        int n = arr.Length;
        RearrangePosNeg(arr, n);
        printArray(arr, n);
    }
}
 
// This code is contributed by vt_m.

PHP

<?php
// PHP program to Rearrange positive 
// and negative numbers in a array
// A utility function to print 
// an array of size n
function printArray($arr, $n)
{
    for ($i = 0; $i < $n; $i++)
        echo($arr[$i] . " ");
}
 
// Function to Rearrange positive and negative
// numbers in a array
function RearrangePosNeg(&$arr, $n)
{
    $key; $j;
    for($i = 1; $i < $n; $i++)
    {
        $key = $arr[$i];
 
        // if current element is positive
        // do nothing
        if ($key > 0)
            continue;
 
        /* if current element is negative,
        shift positive elements of arr[0..i-1],
        to one position to their right */
        $j = $i - 1;
        while ($j >= 0 && $arr[$j] > 0)
        {
            $arr[$j + 1] = $arr[$j];
            $j = $j - 1;
        }
 
        // Put negative element at its right position
        $arr[$j + 1] = $key;
    }
}
 
// Driver program 
{
    $arr = array( -12, 11, -13, -5, 6, -7, 5, -3, -6 );
    $n = sizeof($arr);
    RearrangePosNeg($arr, $n);
    printArray($arr, $n);
 
}
 
// This code is contributed by Code_Mech.

Javascript

<script>
 
// Javascript program to Rearrange positive
// and negative numbers in a array
 
    // A utility function to print
    // an array of size n
    function printArray(arr, n)
    {
        for (let i = 0; i < n; i++)
            document.write(arr[i] + " ");
        document.write("<br />");
    }
  
    // Function to Rearrange positive and negative
    // numbers in a array
     function RearrangePosNeg(arr, n)
    {
        let key, j;
        for (let i = 1; i < n; i++) {
            key = arr[i];
  
            // if current element is positive
            // do nothing
            if (key > 0)
                continue;
  
            /* if current element is negative,
            shift positive elements of arr[0..i-1],
            to one position to their right */
            j = i - 1;
            while (j >= 0 && arr[j] > 0) {
                arr[j + 1] = arr[j];
                j = j - 1;
            }
  
            // Put negative element at its right position
            arr[j + 1] = key;
        }
    }
  
 
// Driver Code
     
        let arr = [ -12, 11, -13, -5, 6, -7, 5, -3, -6 ];
        let n = arr.length;
        RearrangePosNeg(arr, n);
        printArray(arr, n);
         
</script>

Output

-12 -13 -5 -7 -3 -6 11 6 5

Time Complexity: O(n²)
Auxiliary Space: O(1)

We have maintained the order of appearance and have not used any other data structure.

Approach 2: Optimized Merge Sort

Merge method of standard merge sort algorithm can be modified to solve this problem. While merging two sorted halves say left and right, we need to merge in such a way that negative part of left and right sub-array is copied first followed by positive part of left and right sub-array.

Below is the implementation of the idea as shown below as follows:

C++

// C++ program to Rearrange positive and negative
// numbers in a array
#include <iostream>
using namespace std;
 
/* Function to print an array */
void printArray(int A[], int size)
{
    for (int i = 0; i < size; i++)
        cout << A[i] << " ";
    cout << endl;
}
 
// Merges two subarrays of arr[].
// First subarray is arr[l..m]
// Second subarray is arr[m+1..r]
void merge(int arr[], int l, int m, int r)
{
    int i, j, k;
    int n1 = m - l + 1;
    int n2 = r - m;
 
    /* create temp arrays */
    int L[n1], R[n2];
 
    /* Copy data to temp arrays L[] and R[] */
    for (i = 0; i < n1; i++)
        L[i] = arr[l + i];
    for (j = 0; j < n2; j++)
        R[j] = arr[m + 1 + j];
 
    /* Merge the temp arrays back into arr[l..r]*/
    i = 0; // Initial index of first subarray
    j = 0; // Initial index of second subarray
    k = l; // Initial index of merged subarray
 
    // Note the order of appearance of elements should
    // be maintained - we copy elements of left subarray
    // first followed by that of right subarray
 
    // copy negative elements of left subarray
    while (i < n1 && L[i] < 0)
        arr[k++] = L[i++];
 
    // copy negative elements of right subarray
    while (j < n2 && R[j] < 0)
        arr[k++] = R[j++];
 
    // copy positive elements of left subarray
    while (i < n1)
        arr[k++] = L[i++];
 
    // copy positive elements of right subarray
    while (j < n2)
        arr[k++] = R[j++];
}
 
// Function to Rearrange positive and negative
// numbers in a array
void RearrangePosNeg(int arr[], int l, int r)
{
    if (l < r) {
        // Same as (l + r)/2, but avoids overflow for
        // large l and h
        int m = l + (r - l) / 2;
 
        // Sort first and second halves
        RearrangePosNeg(arr, l, m);
        RearrangePosNeg(arr, m + 1, r);
 
        merge(arr, l, m, r);
    }
}
 
/* Driver program to test above functions */
int main()
{
    int arr[] = { -12, 11, -13, -5, 6, -7, 5, -3, -6 };
    int arr_size = sizeof(arr) / sizeof(arr[0]);
 
    RearrangePosNeg(arr, 0, arr_size - 1);
 
    printArray(arr, arr_size);
 
    return 0;
}

Java

// Java program to Rearrange positive
// and negative numbers in a array
import java.io.*;
 
class GFG {
    /* Function to print an array */
    static void printArray(int A[], int size)
    {
        for (int i = 0; i < size; i++)
            System.out.print(A[i] + " ");
        System.out.println();
    }
 
    // Merges two subarrays of arr[].
    // First subarray is arr[l..m]
    // Second subarray is arr[m+1..r]
    static void merge(int arr[], int l, int m, int r)
    {
        int i, j, k;
        int n1 = m - l + 1;
        int n2 = r - m;
 
        /* create temp arrays */
        int L[] = new int[n1];
        int R[] = new int[n2];
 
        /* Copy data to temp arrays L[] and R[] */
        for (i = 0; i < n1; i++)
            L[i] = arr[l + i];
        for (j = 0; j < n2; j++)
            R[j] = arr[m + 1 + j];
 
        /* Merge the temp arrays back into arr[l..r]*/
        // Initial index of first subarray
        i = 0;
 
        // Initial index of second subarray
        j = 0;
 
        // Initial index of merged subarray
        k = l;
 
        // Note the order of appearance of elements should
        // be maintained - we copy elements of left subarray
        // first followed by that of right subarray
 
        // copy negative elements of left subarray
        while (i < n1 && L[i] < 0)
            arr[k++] = L[i++];
 
        // copy negative elements of right subarray
        while (j < n2 && R[j] < 0)
            arr[k++] = R[j++];
 
        // copy positive elements of left subarray
        while (i < n1)
            arr[k++] = L[i++];
 
        // copy positive elements of right subarray
        while (j < n2)
            arr[k++] = R[j++];
    }
 
    // Function to Rearrange positive and negative
    // numbers in a array
    static void RearrangePosNeg(int arr[], int l, int r)
    {
        if (l < r) {
            // Same as (l + r)/2, but avoids overflow for
            // large l and h
            int m = l + (r - l) / 2;
 
            // Sort first and second halves
            RearrangePosNeg(arr, l, m);
            RearrangePosNeg(arr, m + 1, r);
 
            merge(arr, l, m, r);
        }
    }
 
    // Driver program
    public static void main(String[] args)
    {
        int arr[] = { -12, 11, -13, -5, 6, -7, 5, -3, -6 };
        int arr_size = arr.length;
        RearrangePosNeg(arr, 0, arr_size - 1);
        printArray(arr, arr_size);
    }
}
 
// This code is contributed by vt_m.

Python3

# Python3 program to Rearrange positive
# and negative numbers in a array
 
# Function to print an array
 
 
def printArray(A, size):
 
    for i in range(size):
        print(A[i], end=" ")
    print()
 
# Merges two subarrays of arr[].
# First subarray is arr[l..m]
# Second subarray is arr[m + 1..r]
 
 
def merge(arr, l, m, r):
    i, j, k = 0, 0, 0
    n1 = m - l + 1
    n2 = r - m
 
    # create temp arrays */
    L = [arr[l + i] for i in range(n1)]
    R = [arr[m + 1 + j] for j in range(n2)]
 
    # Merge the temp arrays back into arr[l..r]*/
    i = 0  # Initial index of first subarray
    j = 0  # Initial index of second subarray
    k = l  # Initial index of merged subarray
 
    # Note the order of appearance of elements
    # should be maintained - we copy elements
    # of left subarray first followed by that
    # of right subarray
 
    # copy negative elements of left subarray
    while (i < n1 and L[i] < 0):
        arr[k] = L[i]
        k += 1
        i += 1
 
    # copy negative elements of right subarray
    while (j < n2 and R[j] < 0):
        arr[k] = R[j]
        k += 1
        j += 1
 
    # copy positive elements of left subarray
    while (i < n1):
        arr[k] = L[i]
        k += 1
        i += 1
 
    # copy positive elements of right subarray
    while (j < n2):
        arr[k] = R[j]
        k += 1
        j += 1
 
# Function to Rearrange positive and
# negative numbers in a array
 
 
def RearrangePosNeg(arr, l, r):
 
    if(l < r):
 
        # Same as (l + r)/2, but avoids
        # overflow for large l and h
        m = l + (r - l) // 2
 
        # Sort first and second halves
        RearrangePosNeg(arr, l, m)
        RearrangePosNeg(arr, m + 1, r)
 
        merge(arr, l, m, r)
 
 
# Driver Code
arr = [-12, 11, -13, -5,
       6, -7, 5, -3, -6]
arr_size = len(arr)
 
RearrangePosNeg(arr, 0, arr_size - 1)
 
printArray(arr, arr_size)
 
# This code is contributed by
# mohit kumar 29

C#

// C# program to Rearrange positive
// and negative numbers in a array
using System;
 
class GFG {
 
    /* Function to print an array */
    static void printArray(int[] A, int size)
    {
        for (int i = 0; i < size; i++)
            Console.Write(A[i] + " ");
        Console.WriteLine();
    }
 
    // Merges two subarrays of arr[].
    // First subarray is arr[l..m]
    // Second subarray is arr[m+1..r]
    static void merge(int[] arr, int l, int m, int r)
    {
        int i, j, k;
        int n1 = m - l + 1;
        int n2 = r - m;
 
        /* create temp arrays */
        int[] L = new int[n1];
        int[] R = new int[n2];
 
        /* Copy data to temp arrays L[] and R[] */
        for (i = 0; i < n1; i++)
            L[i] = arr[l + i];
        for (j = 0; j < n2; j++)
            R[j] = arr[m + 1 + j];
 
        /* Merge the temp arrays back into arr[l..r]*/
        // Initial index of first subarray
        i = 0;
 
        // Initial index of second subarray
        j = 0;
 
        // Initial index of merged subarray
        k = l;
 
        // Note the order of appearance of elements should
        // be maintained - we copy elements of left subarray
        // first followed by that of right subarray
 
        // copy negative elements of left subarray
        while (i < n1 && L[i] < 0)
            arr[k++] = L[i++];
 
        // copy negative elements of right subarray
        while (j < n2 && R[j] < 0)
            arr[k++] = R[j++];
 
        // copy positive elements of left subarray
        while (i < n1)
            arr[k++] = L[i++];
 
        // copy positive elements of right subarray
        while (j < n2)
            arr[k++] = R[j++];
    }
 
    // Function to Rearrange positive and negative
    // numbers in a array
    static void RearrangePosNeg(int[] arr, int l, int r)
    {
        if (l < r) {
 
            // Same as (l + r)/2, but avoids overflow for
            // large l and h
            int m = l + (r - l) / 2;
 
            // Sort first and second halves
            RearrangePosNeg(arr, l, m);
            RearrangePosNeg(arr, m + 1, r);
 
            merge(arr, l, m, r);
        }
    }
 
    // Driver program
    public static void Main()
    {
        int[] arr = { -12, 11, -13, -5, 6, -7, 5, -3, -6 };
        int arr_size = arr.Length;
        RearrangePosNeg(arr, 0, arr_size - 1);
        printArray(arr, arr_size);
    }
}
 
// This code is contributed by vt_m.

Javascript

<script>
 
// javascript program to Rearrange positive and negative
// numbers in a array  
 
/* Function to print an array */
    function printArray(A , size)
    {
        for (i = 0; i < size; i++)
            document.write(A[i] + " ");
        document.write('<br>');
        ;
    }
 
    /* Function to reverse an array. An array can be
reversed in O(n) time and O(1) space. */
    function reverse(arr , l , r)
    {
        if (l < r) {
            arr = swap(arr, l, r);
            reverse(arr, ++l, --r);
        }
    }
 
    // Merges two subarrays of arr.
    // First subarray is arr[l..m]
    // Second subarray is arr[m+1..r]
    function merge(arr , l , m , r)
    {
    // Initial index of 1st subarray
        var i = l; 
   // Initial index of IInd
        var j = m + 1; 
 
        while (i <= m && arr[i] < 0)
            i++;
 
        // arr[i..m] is positive
 
        while (j <= r && arr[j] < 0)
            j++;
 
        // arr[j..r] is positive
 
        // reverse positive part of
        // left sub-array (arr[i..m])
        reverse(arr, i, m);
 
        // reverse negative part of
        // right sub-array (arr[m+1..j-1])
        reverse(arr, m + 1, j - 1);
 
        // reverse arr[i..j-1]
        reverse(arr, i, j - 1);
    }
 
    // Function to Rearrange positive and negative
    // numbers in a array
    function RearrangePosNeg(arr , l , r)
    {
        if (l < r) {
            // Same as (l+r)/2, but avoids overflow for
            // large l and h
            var m = l + parseInt((r - l) / 2);
 
            // Sort first and second halves
            RearrangePosNeg(arr, l, m);
            RearrangePosNeg(arr, m + 1, r);
 
            merge(arr, l, m, r);
        }
    }
    function swap(arr , i , j)
    {
        var temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
        return arr;
    }
 
    /* Driver code*/
    var arr = [ -12, 11, -13, -5, 6, -7, 5, -3, -6 ];
    var arr_size = arr.length;
 
    RearrangePosNeg(arr, 0, arr_size - 1);
 
    printArray(arr, arr_size);
 
// This code contributed by shikhasingrajput 
 
</script>

Output

-12 -13 -5 -7 -3 -6 11 6 5

Time complexity: O(n log n).
Auxiliary Space: O(n1 + n2 + log n), log n, as implicit stack is used due to recursive call

The problem with this approach is we are using an auxiliary array for merging but we’re not allowed to use any data structure to solve this problem. We can do merging in place without using any data structure. The idea is taken from here.

Let Ln and Lp denote the negative part and positive part of the left sub-array respectively. Similarly, Rn and Rp denote the negative and positive parts of the right sub-array respectively.

Below are the steps to convert [Ln Lp Rn Rp] to [Ln Rn Lp Rp] without using extra space.

1. Reverse Lp and Rn. We get [Lp] -> [Lp'] and [Rn] -> [Rn'] 
    [Ln Lp Rn Rp] -> [Ln Lp’ Rn’ Rp]

2. Reverse [Lp’ Rn’]. We get [Rn Lp].
    [Ln Lp’ Rn’ Rp] -> [Ln Rn Lp Rp]

Below is the implementation of the above idea:

C++

// C++ program to Rearrange positive and negative
// numbers in a array
#include <bits/stdc++.h>
using namespace std;
 
/* Function to print an array */
void printArray(int A[], int size)
{
    for (int i = 0; i < size; i++)
        cout << A[i] << " ";
    cout << endl;
}
 
/* Function to reverse an array. An array can be
reversed in O(n) time and O(1) space. */
void reverse(int arr[], int l, int r)
{
    if (l < r) {
        swap(arr[l], arr[r]);
        reverse(arr, ++l, --r);
    }
}
 
// Merges two subarrays of arr[].
// First subarray is arr[l..m]
// Second subarray is arr[m+1..r]
void merge(int arr[], int l, int m, int r)
{
    int i = l; // Initial index of 1st subarray
    int j = m + 1; // Initial index of IInd
 
    while (i <= m && arr[i] < 0)
        i++;
 
    // arr[i..m] is positive
 
    while (j <= r && arr[j] < 0)
        j++;
 
    // arr[j..r] is positive
 
    // reverse positive part of
    // left sub-array (arr[i..m])
    reverse(arr, i, m);
 
    // reverse negative part of
    // right sub-array (arr[m+1..j-1])
    reverse(arr, m + 1, j - 1);
 
    // reverse arr[i..j-1]
    reverse(arr, i, j - 1);
}
 
// Function to Rearrange positive and negative
// numbers in a array
void RearrangePosNeg(int arr[], int l, int r)
{
    if (l < r) {
        // Same as (l+r)/2, but avoids overflow for
        // large l and h
        int m = l + (r - l) / 2;
 
        // Sort first and second halves
        RearrangePosNeg(arr, l, m);
        RearrangePosNeg(arr, m + 1, r);
 
        merge(arr, l, m, r);
    }
}
 
/* Driver code */
int main()
{
    int arr[] = { -12, 11, -13, -5, 6, -7, 5, -3, -6 };
    int arr_size = sizeof(arr) / sizeof(arr[0]);
 
    RearrangePosNeg(arr, 0, arr_size - 1);
 
    printArray(arr, arr_size);
 
    return 0;
}

Java

// Java program to Rearrange positive and negative
// numbers in a array
import java.io.*;
 
class GFG {
 
    /* Function to print an array */
    static void printArray(int A[], int size)
    {
        for (int i = 0; i < size; i++)
            System.out.print(A[i] + " ");
        System.out.println("");
        ;
    }
 
    /* Function to reverse an array. An array can be
reversed in O(n) time and O(1) space. */
    static void reverse(int arr[], int l, int r)
    {
        if (l < r) {
            arr = swap(arr, l, r);
            reverse(arr, ++l, --r);
        }
    }
 
    // Merges two subarrays of arr[].
    // First subarray is arr[l..m]
    // Second subarray is arr[m+1..r]
    static void merge(int arr[], int l, int m, int r)
    {
        int i = l; // Initial index of 1st subarray
        int j = m + 1; // Initial index of IInd
 
        while (i <= m && arr[i] < 0)
            i++;
 
        // arr[i..m] is positive
 
        while (j <= r && arr[j] < 0)
            j++;
 
        // arr[j..r] is positive
 
        // reverse positive part of
        // left sub-array (arr[i..m])
        reverse(arr, i, m);
 
        // reverse negative part of
        // right sub-array (arr[m+1..j-1])
        reverse(arr, m + 1, j - 1);
 
        // reverse arr[i..j-1]
        reverse(arr, i, j - 1);
    }
 
    // Function to Rearrange positive and negative
    // numbers in a array
    static void RearrangePosNeg(int arr[], int l, int r)
    {
        if (l < r) {
            // Same as (l+r)/2, but avoids overflow for
            // large l and h
            int m = l + (r - l) / 2;
 
            // Sort first and second halves
            RearrangePosNeg(arr, l, m);
            RearrangePosNeg(arr, m + 1, r);
 
            merge(arr, l, m, r);
        }
    }
    static int[] swap(int[] arr, int i, int j)
    {
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
        return arr;
    }
 
    /* Driver code*/
    public static void main(String[] args)
    {
        int arr[] = { -12, 11, -13, -5, 6, -7, 5, -3, -6 };
        int arr_size = arr.length;
 
        RearrangePosNeg(arr, 0, arr_size - 1);
 
        printArray(arr, arr_size);
    }
}
 
// This code has been contributed by 29AjayKumar

Python3

# Python3 program to Rearrange positive
# and negative numbers in an array
 
# Function to print an array
 
 
def printArray(A, size):
 
    for i in range(0, size):
        print(A[i], end=" ")
    print()
 
# Function to reverse an array. An array can
# be reversed in O(n) time and O(1) space.
 
 
def reverse(arr, l, r):
 
    if l < r:
 
        arr[l], arr[r] = arr[r], arr[l]
        l, r = l + 1, r - 1
        reverse(arr, l, r)
 
# Merges two subarrays of arr[].
# First subarray is arr[l..m]
# Second subarray is arr[m + 1..r]
 
 
def merge(arr, l, m, r):
 
    i = l  # Initial index of 1st subarray
    j = m + 1  # Initial index of IInd
 
    while i <= m and arr[i] < 0:
        i += 1
 
    # arr[i..m] is positive
 
    while j <= r and arr[j] < 0:
        j += 1
 
    # arr[j..r] is positive
 
    # reverse positive part of left
    # sub-array (arr[i..m])
    reverse(arr, i, m)
 
    # reverse negative part of right
    # sub-array (arr[m + 1..j-1])
    reverse(arr, m + 1, j - 1)
 
    # reverse arr[i..j-1]
    reverse(arr, i, j - 1)
 
# Function to Rearrange positive
# and negative numbers in a array
 
 
def RearrangePosNeg(arr, l, r):
 
    if l < r:
 
        # Same as (l + r)/2, but avoids
        # overflow for large l and h
        m = l + (r - l) // 2
 
        # Sort first and second halves
        RearrangePosNeg(arr, l, m)
        RearrangePosNeg(arr, m + 1, r)
 
        merge(arr, l, m, r)
 
 
# Driver Code
if __name__ == "__main__":
 
    arr = [-12, 11, -13, -5, 6, -7, 5, -3, -6]
    arr_size = len(arr)
 
    RearrangePosNeg(arr, 0, arr_size - 1)
 
    printArray(arr, arr_size)
 
# This code is contributed by Rituraj Jain

C#

// C# program to Rearrange positive and negative
// numbers in a array
using System;
 
class GFG {
 
    /* Function to print an array */
    static void printArray(int[] A, int size)
    {
        for (int i = 0; i < size; i++)
            Console.Write(A[i] + " ");
        Console.WriteLine("");
        ;
    }
 
    /* Function to reverse an array. An array can be
reversed in O(n) time and O(1) space. */
    static void reverse(int[] arr, int l, int r)
    {
        if (l < r) {
            arr = swap(arr, l, r);
            reverse(arr, ++l, --r);
        }
    }
 
    // Merges two subarrays of arr[].
    // First subarray is arr[l..m]
    // Second subarray is arr[m+1..r]
    static void merge(int[] arr, int l, int m, int r)
    {
        int i = l; // Initial index of 1st subarray
        int j = m + 1; // Initial index of IInd
 
        while (i <= m && arr[i] < 0)
            i++;
 
        // arr[i..m] is positive
 
        while (j <= r && arr[j] < 0)
            j++;
 
        // arr[j..r] is positive
 
        // reverse positive part of
        // left sub-array (arr[i..m])
        reverse(arr, i, m);
 
        // reverse negative part of
        // right sub-array (arr[m+1..j-1])
        reverse(arr, m + 1, j - 1);
 
        // reverse arr[i..j-1]
        reverse(arr, i, j - 1);
    }
 
    // Function to Rearrange positive and negative
    // numbers in a array
    static void RearrangePosNeg(int[] arr, int l, int r)
    {
        if (l < r) {
            // Same as (l+r)/2, but avoids overflow for
            // large l and h
            int m = l + (r - l) / 2;
 
            // Sort first and second halves
            RearrangePosNeg(arr, l, m);
            RearrangePosNeg(arr, m + 1, r);
 
            merge(arr, l, m, r);
        }
    }
    static int[] swap(int[] arr, int i, int j)
    {
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
        return arr;
    }
 
    /* Driver code*/
    public static void Main()
    {
        int[] arr = { -12, 11, -13, -5, 6, -7, 5, -3, -6 };
        int arr_size = arr.Length;
 
        RearrangePosNeg(arr, 0, arr_size - 1);
 
        printArray(arr, arr_size);
    }
}
 
/* This code contributed by PrinciRaj1992 */

Javascript

<script>
// Javascript program to Rearrange positive and negative
// numbers in a array
     
    /* Function to print an array */
    function printArray(A,size)
    {
        for (let i = 0; i < size; i++)
            document.write(A[i] + " ");
        document.write("<br>");
    }
     
    /* Function to reverse an array. An array can be
reversed in O(n) time and O(1) space. */
    function reverse(arr,l,r)
    {
        if (l < r) {
            arr = swap(arr, l, r);
            reverse(arr, ++l, --r);
        }
    }
     
    // Merges two subarrays of arr[].
    // First subarray is arr[l..m]
    // Second subarray is arr[m+1..r]
    function merge(arr,l,m,r)
    {
        let i = l; // Initial index of 1st subarray
        let j = m + 1; // Initial index of IInd
  
        while (i <= m && arr[i] < 0)
            i++;
  
        // arr[i..m] is positive
  
        while (j <= r && arr[j] < 0)
            j++;
  
        // arr[j..r] is positive
  
        // reverse positive part of
        // left sub-array (arr[i..m])
        reverse(arr, i, m);
  
        // reverse negative part of
        // right sub-array (arr[m+1..j-1])
        reverse(arr, m + 1, j - 1);
  
        // reverse arr[i..j-1]
        reverse(arr, i, j - 1);
    }
     
    // Function to Rearrange positive and negative
    // numbers in a array
    function RearrangePosNeg(arr,l,r)
    {
        if (l < r) {
            // Same as (l+r)/2, but avoids overflow for
            // large l and h
            let m = l + Math.floor((r - l) / 2);
  
            // Sort first and second halves
            RearrangePosNeg(arr, l, m);
            RearrangePosNeg(arr, m + 1, r);
  
            merge(arr, l, m, r);
        }
    }
     
    function swap(arr,i,j)
    {
        let temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
        return arr;
    }
     
    /* Driver code*/
    let arr=[-12, 11, -13, -5, 6, -7, 5, -3, -6 ];
    let arr_size = arr.length;
    RearrangePosNeg(arr, 0, arr_size - 1);
  
    printArray(arr, arr_size);
     
 
// This code is contributed by unknown2108
 
</script>

Output

-12 -13 -5 -7 -3 -6 11 6 5

Time complexity: O(n log n), O(Log n) space for recursive calls, and no additional data structure.
Auxiliary Space: O(log n), as implicit stack is used due to recursive call

Approach 4: Using Sliding Window with two pointer technique

This technique utilises sliding window of positive numbers to shift negative numbers to the start of the window, while moving forward.

C++

#include <iostream>
using namespace std;
 
void rearrangePosNegWithOrder(int *arr, int size)
{
   int i = 0, j = 0;
   while (j < size) {
       if (arr[j] >= 0) {
           j++;
       }
       else {
           for (int k = j; k > i; k--) {
               int temp = arr[k];
               arr[k] = arr[k - 1];
               arr[k - 1] = temp;
           }
           i++;
           j++;
       }
   }
}
 
int main()
{
 
   int arr[] = { -12, 11, -13, -5, 6, -7, 5, -3, -6 };
   int size = *(&arr + 1) - arr;
   rearrangePosNegWithOrder(arr, size);
   for (int i : arr) {
       cout << i;
       cout << " ";
   }
   return 0;
}

Java

import java.io.*;
 
class GFG {
 
   // Here the size of window increases as it encounters
   // positive numbers
   public static void rearrangePosNegWithOrder(int[] arr)
   {
       int i = 0, j = 0;
       while (j < arr.length) {
           if (arr[j] >= 0) {
               j++;
           }
           else {
               for (int k = j; k > i; k--) {
                   int temp = arr[k];
                   arr[k] = arr[k - 1];
                   arr[k - 1] = temp;
               }
               i++;
               j++;
           }
       }
   }
   public static void main(String[] args)
   {
       int arr[] = { -12, 11, -13, -5, 6, -7, 5, -3, -6 };
 
       rearrangePosNegWithOrder(arr);
 
       for (int i : arr) {
           System.out.print(i + " ");
       }
   }
}

Python3

def rearrangePosNegWithOrder(arr, size):
    i = 0
    j = 0
    while(j < size):
        if(arr[j] >= 0):
            j += 1
        else:
            for k in range(j,i,-1):
                temp = arr[k]
                arr[k] = arr[k - 1]
                arr[k - 1] = temp   
            i += 1
            j += 1
    return arr
   
# driver code
arr = [-12, 11, -13, -5, 6, -7, 5, -3, -6 ]
size = len(arr)
aux = rearrangePosNegWithOrder(arr, size)
for i in aux: 
    print(i,end=" ")
 
# This code is contributed by Vibhu Karnwal

C#

// C# code addition for the above approach
using System;
 
public class GFG 
{
 
  // Here the size of window increases as it encounters
  // positive numbers
  public static void rearrangePosNegWithOrder(int[] arr)
  {
    int i = 0, j = 0;
    while (j < arr.Length) {
      if (arr[j] >= 0) {
        j++;
      }
      else {
        for (int k = j; k > i; k--) {
          int temp = arr[k];
          arr[k] = arr[k - 1];
          arr[k - 1] = temp;
        }
        i++;
        j++;
      }
    }
  }
 
  static public void Main()
  {
 
    // Code
    int[] arr = { -12, 11, -13, -5, 6, -7, 5, -3, -6 };
    rearrangePosNegWithOrder(arr);
    foreach(int i in arr) { Console.Write(i + " "); }
  }
}
 
// This code is contributed by lokesh

Javascript

// JS code for above approach
 
function rearrangePosNegWithOrder(arr, size) {
    let i = 0, j = 0;
    while (j < size) {
        if (arr[j] >= 0) {
            j++;
        }
        else {
            for (let k = j; k > i; k--) {
                let temp = arr[k];
                arr[k] = arr[k - 1];
                arr[k - 1] = temp;
            }
            i++;
            j++;
        }
    }
}
 
let arr = [-12, 11, -13, -5, 6, -7, 5, -3, -6];
let size = arr.length;
rearrangePosNegWithOrder(arr, size);
for (let i = 0; i < size; i++) {
    console.log(arr[i]);
}
 
// This code is contributed by adityamaharshi21

Output

-12 -13 -5 -7 -3 -6 11 6 5

Time Complexity: O(n*window)
Auxiliary Space: O(1), since no extra space has been taken.

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