Maximize the subarray sum after multiplying all elements of any subarray with X
Given an array arr[] of N integers and an integer X. We can choose any sub-array and multiply all its element by X. After multiplication, find the sub-array with the maximum sum. The task is to multiply the sub-array in such a way that the final sub-array sum is maximized.
Examples:
Input: arr[] = { -3, 8, -2, 1, -6 }, X = -1
Output: 15
Choose the sub-array with {-2, 1, -6} and multiply X.
Now the new array is {-3, 8, 2, -1, 6} whose maximum sub-array sum is 15.
Input: arr[] = {1, 2, 4, -10}, X = 2
Output: 14
Approach: The problem cannot be solved using a greedy approach. Greedy approach fails in many cases one of them being a[] = { -3, 8, -2, 1, 6 } and x = -1. We will use Dynamic Programming to solve the above problem. Let dp[ind][state], where ind is the current index in the array and there are 3 states.
- The first state defines that no sub-array has been chosen till index ind to be multiplied with X.
- The second state defines that the current element at index ind is in the sub-array which is multiplied with X.
- The third state defines that the sub-array has already been chosen.
Kadane’s algorithm has been used along with DP to get the maximum subarray sum simultaneously.
Below is the implementation of the above approach:
C++
// C++ implementation of the approach#include <bits/stdc++.h>using namespace std;#define N 5// Function to return the maximum sumint func(int idx, int cur, int a[], int dp[N][3], int n, int x){ // Base case if (idx == n) return 0; // If already calculated if (dp[idx][cur] != -1) return dp[idx][cur]; int ans = 0; // If no elements have been chosen if (cur == 0) { // Do not choose any element and use // Kadane's algorithm by taking max ans = max(ans, a[idx] + func(idx + 1, 0, a, dp, n, x)); // Choose the sub-array and multiply x ans = max(ans, x * a[idx] + func(idx + 1, 1, a, dp, n, x)); } else if (cur == 1) { // Choose the sub-array and multiply x ans = max(ans, x * a[idx] + func(idx + 1, 1, a, dp, n, x)); // End the sub-array multiplication ans = max(ans, a[idx] + func(idx + 1, 2, a, dp, n, x)); } else // No more multiplication ans = max(ans, a[idx] + func(idx + 1, 2, a, dp, n, x)); // Memoize and return the answer return dp[idx][cur] = ans;}// Function to get the maximum sumint getMaximumSum(int a[], int n, int x){ // Initialize dp with -1 int dp[n][3]; memset(dp, -1, sizeof dp); // Iterate from every position and find the // maximum sum which is possible int maxi = 0; for (int i = 0; i < n; i++) maxi = max(maxi, func(i, 0, a, dp, n, x)); return maxi;}// Driver codeint main(){ int a[] = { -3, 8, -2, 1, -6 }; int n = sizeof(a) / sizeof(a[0]); int x = -1; cout << getMaximumSum(a, n, x); return 0;} |
Java
// Java implementation of the approachclass GFG{ static int N = 5;// Function to return the maximum sumstatic int func(int idx, int cur, int a[], int dp[][], int n, int x){ // Base case if (idx == n) { return 0; } // If already calculated if (dp[idx][cur] != -1) { return dp[idx][cur]; } int ans = 0; // If no elements have been chosen if (cur == 0) { // Do not choose any element and use // Kadane's algorithm by taking max ans = Math.max(ans, a[idx] + func(idx + 1, 0, a, dp, n, x)); // Choose the sub-array and multiply x ans = Math.max(ans, x * a[idx] + func(idx + 1, 1, a, dp, n, x)); } else if (cur == 1) { // Choose the sub-array and multiply x ans = Math.max(ans, x * a[idx] + func(idx + 1, 1, a, dp, n, x)); // End the sub-array multiplication ans = Math.max(ans, a[idx] + func(idx + 1, 2, a, dp, n, x)); } else // No more multiplication { ans = Math.max(ans, a[idx] + func(idx + 1, 2, a, dp, n, x)); } // Memoize and return the answer return dp[idx][cur] = ans;}// Function to get the maximum sumstatic int getMaximumSum(int a[], int n, int x){ // Initialize dp with -1 int dp[][] = new int[n][3]; for (int i = 0; i < n; i++) { for (int j = 0; j < 3; j++) { dp[i][j] = -1; } } // Iterate from every position and find the // maximum sum which is possible int maxi = 0; for (int i = 0; i < n; i++) { maxi = Math.max(maxi, func(i, 0, a, dp, n, x)); } return maxi;}// Driver codepublic static void main(String[] args) { int a[] = {-3, 8, -2, 1, -6}; int n = a.length; int x = -1; System.out.println(getMaximumSum(a, n, x));}}// This code has been contributed by 29AjayKumar |
Python3
# Python3 implementation of the approachN = 5# Function to return the maximum sumdef func(idx, cur, a, dp, n, x) : # Base case if (idx == n) : return 0 # If already calculated if (dp[idx][cur] != -1): return dp[idx][cur] ans = 0 # If no elements have been chosen if (cur == 0) : # Do not choose any element and use # Kadane's algorithm by taking max ans = max(ans, a[idx] + func(idx + 1, 0, a, dp, n, x)) # Choose the sub-array and multiply x ans = max(ans, x * a[idx] + func(idx + 1, 1, a, dp, n, x)) elif (cur == 1) : # Choose the sub-array and multiply x ans = max(ans, x * a[idx] + func(idx + 1, 1, a, dp, n, x)) # End the sub-array multiplication ans = max(ans, a[idx] + func(idx + 1, 2, a, dp, n, x)) else : # No more multiplication ans = max(ans, a[idx] + func(idx + 1, 2, a, dp, n, x)) # Memoize and return the answer dp[idx][cur] = ans return dp[idx][cur] # Function to get the maximum sumdef getMaximumSum(a, n, x) : # Initialize dp with -1 dp = [[-1 for i in range(3)] for j in range(n)] # Iterate from every position and find the # maximum sum which is possible maxi = 0 for i in range (0, n) : maxi = max(maxi, func(i, 0, a, dp, n, x)) return maxi # Driver codea = [ -3, 8, -2, 1, -6 ] n = len(a) x = -1print(getMaximumSum(a, n, x)) # This code is contributed by ihritik |
C#
// C# implementation of the approachusing System;class GFG{ static int N = 5;// Function to return the maximum sumstatic int func(int idx, int cur, int []a, int [,]dp, int n, int x){ // Base case if (idx == n) { return 0; } // If already calculated if (dp[idx,cur] != -1) { return dp[idx,cur]; } int ans = 0; // If no elements have been chosen if (cur == 0) { // Do not choose any element and use // Kadane's algorithm by taking max ans = Math.Max(ans, a[idx] + func(idx + 1, 0, a, dp, n, x)); // Choose the sub-array and multiply x ans = Math.Max(ans, x * a[idx] + func(idx + 1, 1, a, dp, n, x)); } else if (cur == 1) { // Choose the sub-array and multiply x ans = Math.Max(ans, x * a[idx] + func(idx + 1, 1, a, dp, n, x)); // End the sub-array multiplication ans = Math.Max(ans, a[idx] + func(idx + 1, 2, a, dp, n, x)); } else // No more multiplication { ans = Math.Max(ans, a[idx] + func(idx + 1, 2, a, dp, n, x)); } // Memoize and return the answer return dp[idx,cur] = ans;}// Function to get the maximum sumstatic int getMaximumSum(int []a, int n, int x){ // Initialize dp with -1 int [,]dp = new int[n,3]; for (int i = 0; i < n; i++) { for (int j = 0; j < 3; j++) { dp[i,j] = -1; } } // Iterate from every position and find the // maximum sum which is possible int maxi = 0; for (int i = 0; i < n; i++) { maxi = Math.Max(maxi, func(i, 0, a, dp, n, x)); } return maxi;}// Driver codepublic static void Main(String[] args) { int []a = {-3, 8, -2, 1, -6}; int n = a.Length; int x = -1; Console.WriteLine(getMaximumSum(a, n, x));}}/* This code contributed by PrinciRaj1992 */ |
Javascript
<script>// JavaScript implementation of the approach var N = 5; // Function to return the maximum sum function func(idx , cur , a , dp , n , x) { // Base case if (idx == n) { return 0; } // If already calculated if (dp[idx][cur] != -1) { return dp[idx][cur]; } var ans = 0; // If no elements have been chosen if (cur == 0) { // Do not choose any element and use // Kadane's algorithm by taking max ans = Math.max(ans, a[idx] + func(idx + 1, 0, a, dp, n, x)); // Choose the sub-array and multiply x ans = Math.max(ans, x * a[idx] + func(idx + 1, 1, a, dp, n, x)); } else if (cur == 1) { // Choose the sub-array and multiply x ans = Math.max(ans, x * a[idx] + func(idx + 1, 1, a, dp, n, x)); // End the sub-array multiplication ans = Math.max(ans, a[idx] + func(idx + 1, 2, a, dp, n, x)); } else // No more multiplication { ans = Math.max(ans, a[idx] + func(idx + 1, 2, a, dp, n, x)); } // Memoize and return the answer return dp[idx][cur] = ans; } // Function to get the maximum sum function getMaximumSum(a , n , x) { // Initialize dp with -1 var dp = Array(n).fill().map(()=>Array(3).fill(0)); for (i = 0; i < n; i++) { for (j = 0; j < 3; j++) { dp[i][j] = -1; } } // Iterate from every position and find the // maximum sum which is possible var maxi = 0; for (i = 0; i < n; i++) { maxi = Math.max(maxi, func(i, 0, a, dp, n, x)); } return maxi; } // Driver code var a = [ -3, 8, -2, 1, -6 ]; var n = a.length; var x = -1; document.write(getMaximumSum(a, n, x));// This code contributed by Rajput-Ji</script> |
PHP
<?php// PHP implementation of the approach $N = 5; // Function to return the maximum sum function func($idx, $cur, $a, $dp, $n, $x) { // Base case if ($idx == $n) return 0; // If already calculated if ($dp[$idx][$cur] != -1) return $dp[$idx][$cur]; $ans = 0; // If no elements have been chosen if ($cur == 0) { // Do not choose any element and use // Kadane's algorithm by taking max $ans = max($ans, $a[$idx] + func($idx + 1, 0, $a, $dp, $n, $x)); // Choose the sub-array and multiply x $ans = max($ans, $x * $a[$idx] + func($idx + 1, 1, $a, $dp, $n, $x)); } else if ($cur == 1) { // Choose the sub-array and multiply x $ans = max($ans, $x * $a[$idx] + func($idx + 1, 1, $a, $dp, $n, $x)); // End the sub-array multiplication $ans = max($ans, $a[$idx] + func($idx + 1, 2, $a, $dp, $n, $x)); } else // No more multiplication $ans = max($ans, $a[$idx] + func($idx + 1, 2, $a, $dp,$n, $x)); // Memoize and return the answer return $dp[$idx][$cur] = $ans; } // Function to get the maximum sum function getMaximumSum($a, $n, $x) { // Initialize dp with -1 $dp = array(array()) ; for($i = 0; $i < $n; $i++) { for($j = 0; $j < 3; $j++) { $dp[$i][$j] = -1; } } // Iterate from every position and find the // maximum sum which is possible $maxi = 0; for ($i = 0; $i < $n; $i++) $maxi = max($maxi, func($i, 0, $a, $dp, $n, $x)); return $maxi; } // Driver code $a = array( -3, 8, -2, 1, -6 ); $n = count($a) ; $x = -1; echo getMaximumSum($a, $n, $x); // This code is contributed by Ryuga?> |
Output
15
Time Complexity: O(N * 3)
Auxiliary Space: O(N * 3)
Efficient approach : Using DP Tabulation method ( Iterative approach )
The approach to solve this problem is same but DP tabulation(bottom-up) method is better then Dp + memoization(top-down) because memoization method needs extra stack space of recursion calls.
Steps to solve this problem :
- Create a DP to store the solution of the subproblems.
- Initialize the DP with base cases
- Now Iterate over subproblems to get the value of current problem form previous computation of subproblems stored in DP.
- Create a variable ans to keep track of values of DP in each condition.
- After iteration from loop create a variable maxi to store the maximum sum and update it by iterate over Dp.
- Return the final solution stored in maxi.
Implementation :
C++
#include <bits/stdc++.h>using namespace std;#define N 5// Function to return the maximum sumint getMaximumSum(int a[], int n, int x){ int dp[n][3]; // Initializing the dp array for(int i=0; i<n; i++){ dp[i][0] = a[i]; dp[i][1] = a[i]*x; dp[i][2] = a[i]; } // Applying the recurrence relation for(int i=n-2; i>=0; i--){ for(int j=0; j<3; j++){ // to track the answer in each condition int ans = 0; if(j==0){ ans = max(dp[i][j], dp[i+1][j]+a[i]); ans = max(ans, dp[i+1][j+1]+x*a[i]); } else if(j==1){ ans = max(dp[i][j], dp[i+1][j]+x*a[i]); ans = max(ans, dp[i+1][j+1]+a[i]); } else{ ans = max(dp[i][j], dp[i+1][j]+a[i]); } // update DP dp[i][j] = ans; } } // Finding the maximum sum from dp array int maxi = 0; for (int i = 0; i < n; i++) maxi = max(maxi, dp[i][0]); // return final answer return maxi;}// Driver codeint main(){ int a[] = { -3, 8, -2, 1, -6 }; int n = sizeof(a) / sizeof(a[0]); int x = -1; // function call cout << getMaximumSum(a, n, x); return 0;} |
Java
import java.util.*;public class Main { public static int getMaximumSum(int[] a, int n, int x) { // Initializing the dp array int[][] dp = new int[n][3]; for (int i = 0; i < n; i++) { dp[i][0] = a[i]; dp[i][1] = a[i] * x; dp[i][2] = a[i]; } // Applying the recurrence relation for (int i = n - 2; i >= 0; i--) { for (int j = 0; j < 3; j++) { // to track the answer in each condition int ans = 0; if (j == 0) { ans = Math.max(dp[i][j], dp[i + 1][j] + a[i]); ans = Math.max(ans, dp[i + 1][j + 1] + x * a[i]); } else if (j == 1) { ans = Math.max(dp[i][j], dp[i + 1][j] + x * a[i]); ans = Math.max(ans, dp[i + 1][j + 1] + a[i]); } else { ans = Math.max(dp[i][j], dp[i + 1][j] + a[i]); } // update DP dp[i][j] = ans; } } // Finding the maximum sum from dp array int maxi = 0; for (int i = 0; i < n; i++) { maxi = Math.max(maxi, dp[i][0]); } // return final answer return maxi; } public static void main(String[] args) { int[] a = { -3, 8, -2, 1, -6 }; int n = a.length; int x = -1; // function call System.out.println(getMaximumSum(a, n, x)); }}// This code is contributed by user_dtewbxkn77n |
Python3
# Function to return the maximum sumdef getMaximumSum(a, n, x): # Initializing the dp array dp = [[0 for j in range(3)] for i in range(n)] for i in range(n): dp[i][0] = a[i] dp[i][1] = a[i] * x dp[i][2] = a[i] # Applying the recurrence relation for i in range(n-2, -1, -1): for j in range(3): # to track the answer in each condition ans = 0 if j == 0: ans = max(dp[i][j], dp[i+1][j]+a[i]) ans = max(ans, dp[i+1][j+1]+x*a[i]) elif j == 1: ans = max(dp[i][j], dp[i+1][j]+x*a[i]) ans = max(ans, dp[i+1][j+1]+a[i]) else: ans = max(dp[i][j], dp[i+1][j]+a[i]) # update DP dp[i][j] = ans # Finding the maximum sum from dp array maxi = 0 for i in range(n): maxi = max(maxi, dp[i][0]) # return final answer return maxi# Driver codeif __name__ == '__main__': a = [-3, 8, -2, 1, -6] n = len(a) x = -1 # function call print(getMaximumSum(a, n, x)) |
C#
using System;class Program { const int N = 5; // Function to return the maximum sum static int GetMaximumSum(int[] a, int n, int x) { int[, ] dp = new int[n, 3]; // Initializing the dp array for (int i = 0; i < n; i++) { dp[i, 0] = a[i]; dp[i, 1] = a[i] * x; dp[i, 2] = a[i]; } // Applying the recurrence relation for (int i = n - 2; i >= 0; i--) { for (int j = 0; j < 3; j++) { // to track the answer in each condition int ans = 0; if (j == 0) { ans = Math.Max(dp[i, j], dp[i + 1, j] + a[i]); ans = Math.Max(ans, dp[i + 1, j + 1] + x * a[i]); } else if (j == 1) { ans = Math.Max(dp[i, j], dp[i + 1, j] + x * a[i]); ans = Math.Max(ans, dp[i + 1, j + 1] + a[i]); } else { ans = Math.Max(dp[i, j], dp[i + 1, j] + a[i]); } // update DP dp[i, j] = ans; } } // Finding the maximum sum from dp array int maxi = 0; for (int i = 0; i < n; i++) { maxi = Math.Max(maxi, dp[i, 0]); } // return final answer return maxi; } // Driver code static void Main() { int[] a = { -3, 8, -2, 1, -6 }; int n = a.Length; int x = -1; // function call Console.WriteLine(GetMaximumSum(a, n, x)); }} |
Javascript
// Function to return the maximum sumfunction getMaximumSum(a, n, x) { // Initializing the dp array let dp = Array.from({ length: n }, () => Array(3).fill(0)); for (let i = 0; i < n; i++) { dp[i][0] = a[i]; dp[i][1] = a[i] * x; dp[i][2] = a[i]; } // Applying the recurrence relation for (let i = n - 2; i >= 0; i--) { for (let j = 0; j < 3; j++) { // to track the answer in each condition let ans = 0; if (j === 0) { ans = Math.max(dp[i][j], dp[i + 1][j] + a[i]); ans = Math.max(ans, dp[i + 1][j + 1] + x * a[i]); } else if (j === 1) { ans = Math.max(dp[i][j], dp[i + 1][j] + x * a[i]); ans = Math.max(ans, dp[i + 1][j + 1] + a[i]); } else { ans = Math.max(dp[i][j], dp[i + 1][j] + a[i]); } // update DP dp[i][j] = ans; } } // Finding the maximum sum from dp array let maxi = 0; for (let i = 0; i < n; i++) { maxi = Math.max(maxi, dp[i][0]); } // return final answer return maxi;}// Driver codelet a = [-3, 8, -2, 1, -6];let n = a.length;let x = -1;// function callconsole.log(getMaximumSum(a, n, x)); |
Output:
15
Time Complexity: O(N * 3)
Auxiliary Space: O(N * 3)
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