Check if the given Binary Tree have a Subtree with equal no of 1’s and 0’s

Given a Binary Tree having data at nodes as either 0’s or 1’s. The task is to find out whether there exists a subtree having an equal number of 1’s and 0’s.


Input :

Output : True
There are two subtrees present in the above tree where the number of 1’s is equal to the number of 0’s.

Input :

Output : False
There is no such subtree present which has the number of 1’s equal to number of 0’s

Approach: The idea is to change the data 0’s of the tree to -1. So that it becomes very easy to find the subtree having equal number of 0’s and 1’s. After converting all 0’s to -1, create a sum tree. After creating the sum tree, each node will contain the sum of all node lying under it.

Traverse the tree again and find if there is a node having 0 sum, it means that there is a subtree that has the equal number of 1’s and -1’s, i.e. equal number of 1’s and 0’s.

Below is the implementation of the above approach:





// C++ program to check if there exist a
// subtree with equal number of 1's and 0's
#include <bits/stdc++.h>
using namespace std;
// Binary Tree Node
struct node {
    int data;
    struct node *right, *left;
// Utility function to create a new node
struct node* newnode(int key)
    struct node* temp = new node;
    temp->data = key;
    temp->right = NULL;
    temp->left = NULL;
    return temp;
// Function to convert all 0's in the
// tree to -1
void convert(struct node* root)
    if (root == NULL) {
    // Move to right subtree
    // Replace the 0's with -1 in the tree
    if (root->data == 0) {
        root->data = -1;
    // Move to left subtree
// Function to convert the tree to a SUM tree
int sum_tree(struct node* root)
    int a = 0, b = 0;
    if (root == NULL) {
        return 0;
    a = sum_tree(root->left);
    b = sum_tree(root->right);
    root->data = root->data + a + b;
    return root->data;
// Function to check if there exists a subtree
// with equal no of 1s and 0s
int checkSubtree(struct node* root, int d)
    if (root == NULL) {
        return 0;
    // Check if there is a subtree with equal
    // 1s and 0s or not
    if (d == 0) {
        d = checkSubtree(root->left, d);
    if (root->data == 0) {
        d = 1;
        return d;
    if (d == 0) {
        d = checkSubtree(root->right, d);
    return d;
// Driver Code
int main()
    // Create the Binary Tree
    struct node* root = newnode(1);
    root->right = newnode(0);
    root->right->right = newnode(1);
    root->right->right->right = newnode(1);
    root->left = newnode(0);
    root->left->left = newnode(1);
    root->left->left->left = newnode(1);
    root->left->right = newnode(0);
    root->left->right->left = newnode(1);
    root->left->right->left->left = newnode(1);
    root->left->right->right = newnode(0);
    root->left->right->right->left = newnode(0);
    root->left->right->right->left->left = newnode(1);
    // Convert all 0s in tree to -1
    // Convert the tree into a SUM tree
    // Check if required Subtree exists
    int d = 0;
    if (checkSubtree(root, d)) {
        cout << "True" << endl;
    else {
        cout << "False" << endl;
    return 0;




Time Complexity: O(N)
Space Complexity: O(1)

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