Print Binary Tree levels in sorted order | Set 2 (Using set)

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Given a tree, print the level order traversal in sorted order.

Examples :

Input :     7
          /    \
        6       5
       / \     / \
      4  3    2   1
      
Output : 
7
5 6
1 2 3 4 

Input :     7
          /    \
        16       1
       / \      
      4   13    
      
Output :
7 
1 16
4 13

We have discussed a priority queue based solution in below post.
Print Binary Tree levels in sorted order | Set 1 (Using Priority Queue)

In this post, a set (which is implemented using balanced binary search tree) based solution is discussed.

Approach :

Start level order traversal of tree.
Store all the nodes in a set(or any other similar data structures).
Print elements of set.

Implementation:

C++

// CPP code to print level order 
// traversal in sorted order
#include <bits/stdc++.h>
using namespace std;
 
struct Node {
    int data;
    Node* left;
    Node* right;
    Node(int dat = 0)
        : data(dat), left(nullptr), 
          right(nullptr)
    {
    }
};
 
// Function to print sorted 
// level order traversal
void sorted_level_order(Node* root)
{
    queue<Node*> q;
    set<int> s;
 
    q.push(root);
    q.push(nullptr);
 
    while (q.empty() == false) {
        Node* tmp = q.front();
        q.pop();
 
        if (tmp == nullptr) {
            if (s.empty() == true)
                break;
            for (set<int>::iterator it =
                 s.begin();it != s.end(); ++it) 
                cout << *it << " ";
            q.push(nullptr);
            s.clear();
        }
        else {
            s.insert(tmp->data);
 
            if (tmp->left != nullptr)
                q.push(tmp->left);
            if (tmp->right != nullptr)
                q.push(tmp->right);
        }
    }
}
 
// Driver code
int main()
{
    Node* root = new Node(7);
    root->left = new Node(6);
    root->right = new Node(5);
    root->left->left = new Node(4);
    root->left->right = new Node(3);
    root->right->left = new Node(2);
    root->right->right = new Node(1);    
    sorted_level_order(root);    
    return 0;    
}

Java

// Java code to print level order 
// traversal in sorted order
import java.util.*; 
import java.util.HashSet; 
 
class GFG 
{ 
static class Node 
{ 
    int data; 
    Node left, right; 
};
static Node newNode(int data) 
{ 
    Node node = new Node(); 
    node.data = data; 
    node.left = node.right = null; 
    return (node); 
} 
 
// Function to print sorted 
// level order traversal
static void sorted_level_order(Node root)
{
    Queue<Node> q = new LinkedList<>(); 
    Set<Integer> s = new HashSet<Integer>();
    q.add(root);
    q.add(null);
 
    while (!q.isEmpty())
    {
        Node tmp = q.peek(); 
            q.remove(); 
 
        if (tmp == null)
        {
            if (s.isEmpty())
                break;
            Iterator value = s.iterator(); 
            while (value.hasNext())
            { 
                System.out.print(value.next() + " "); 
            } 
            q.add(null);
            s.clear();
        }
        else
        {
            s.add(tmp.data);
 
            if (tmp.left != null)
                q.add(tmp.left);
            if (tmp.right != null)
                q.add(tmp.right);
        }
    }
}
 
// Driver Code
public static void main(String[] args) 
{
    Node root = newNode(7);
    root.left = newNode(6);
    root.right = newNode(5);
    root.left.left = newNode(4);
    root.left.right = newNode(3);
    root.right.left = newNode(2);
    root.right.right = newNode(1); 
    sorted_level_order(root); 
}
}
 
// This code is contributed by SHUBHAMSINGH10

Python3

# Python3 program to print level order 
# traversal in sorted order
 
# Helper function that allocates a new 
# node with the given data and None 
# left and right pointers.                                     
class newNode: 
 
    # Construct to create a new node 
    def __init__(self, key): 
        self.data = key
        self.left = None
        self.right = None
 
# Function to print sorted 
# level order traversal
def sorted_level_order( root):
 
    q = []
    s = set()
 
    q.append(root)
    q.append(None)
 
    while (len(q)):
        tmp = q[0]
        q.pop(0)
 
        if (tmp == None): 
            if (not len(s)):
                break
            for i in s: 
                print(i, end = " ")
            q.append(None)
            s = set()
         
        else :
            s.add(tmp.data)
 
            if (tmp.left != None):
                q.append(tmp.left)
            if (tmp.right != None):
                q.append(tmp.right)
 
# Driver Code 
if __name__ == '__main__':
     
    """ 
    Let us create Binary Tree shown
    in above example """
    root = newNode(7)
    root.left = newNode(6)
    root.right = newNode(5)
    root.left.left = newNode(4)
    root.left.right = newNode(3)
    root.right.left = newNode(2)
    root.right.right = newNode(1)
    sorted_level_order(root)
 
# This code is contributed by
# Shubham Singh(SHUBHAMSINGH10)

C#

// C# code to print level order 
// traversal in sorted order
using System;
using System.Collections.Generic;
 
class GFG 
{ 
public class Node 
{ 
    public int data; 
    public Node left, right; 
};
 
static Node newNode(int data) 
{ 
    Node node = new Node(); 
    node.data = data; 
    node.left = node.right = null; 
    return (node); 
} 
 
// Function to print sorted 
// level order traversal
static void sorted_level_order(Node root)
{
    Queue<Node> q = new Queue<Node>(); 
    SortedSet<int> s = new SortedSet<int>();
    q.Enqueue(root);
    q.Enqueue(null);
 
    while (q.Count != 0)
    {
        Node tmp = q.Peek(); 
            q.Dequeue(); 
 
        if (tmp == null)
        {
            if (s.Count == 0)
                break;
            foreach (int v in s)
            { 
                Console.Write(v + " "); 
            } 
            q.Enqueue(null);
            s.Clear();
        }
        else
        {
            s.Add(tmp.data);
 
            if (tmp.left != null)
                q.Enqueue(tmp.left);
            if (tmp.right != null)
                q.Enqueue(tmp.right);
        }
    }
}
 
// Driver Code
public static void Main(String[] args) 
{
    Node root = newNode(7);
    root.left = newNode(6);
    root.right = newNode(5);
    root.left.left = newNode(4);
    root.left.right = newNode(3);
    root.right.left = newNode(2);
    root.right.right = newNode(1); 
    sorted_level_order(root); 
}
}
 
// This code is contributed by 29AjayKumar

Javascript

<script>
// Javascript code to print level order 
// traversal in sorted order
var SortedSet = require("collections/sorted-set");
 
class Node 
{
    constructor()
    {
        this.data=0;
        this.left=this.right=null;
    }
}
 
function newNode(data)
{
    let node = new Node(); 
    node.data = data; 
    node.left = node.right = null; 
    return (node); 
}
 
// Function to print sorted 
// level order traversal
function sorted_level_order(root)
{
    let q = [];
    let s = new SortedSet();
    q.push(root);
    q.push(null);
   
    while (q.length!=0)
    {
        let tmp = q.shift(); 
             
       
        if (tmp == null)
        {
            if (s.size==0)
                break;
            for(let i of s.values())
            {
                document.write(i+" ");
            }
            q.push(null);
            s.clear();
        }
        else
        {
            s.add(tmp.data);
   
            if (tmp.left != null)
                q.push(tmp.left);
            if (tmp.right != null)
                q.push(tmp.right);
        }
    }
}
 
// Driver Code
let root = newNode(7);
root.left = newNode(6);
root.right = newNode(5);
root.left.left = newNode(4);
root.left.right = newNode(3);
root.right.left = newNode(2);
root.right.right = newNode(1); 
sorted_level_order(root); 
 
 
// This code is contributed by rag2127
</script>

Output:

7 5 6 1 2 3 4

Time Complexity: O(n*log(n)) where n is the number of nodes in the binary tree.
Auxiliary Space: O(n) where n is the number of nodes in the binary tree.

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