Subtree with given sum in a Binary Tree

You are given a binary tree and a given sum. The task is to check if there exist a subtree whose sum of all nodes is equal to the given sum.


Examples:

// For above tree
Input : sum = 22
Output: "Yes"
// sum of all nodes of subtree {1, 7, 12, 2} = 22

Input : sum = 15
Output: "No"
// no subtree with given sum exist

The idea is to traverse tree in Postorder fashion because here we have to think bottom-up . First calculate the sum of left subtree then right subtree and check if sum_left + sum_right + cur_node = sum is satisfying the condition that means any subtree with given sum exist. Below is the recursive implementation of algorithm.

// C++ program to find if there is a subtree with
// given sum
#include<bits/stdc++.h>
using namespace std;

/* A binary tree node has data, pointer to left child
   and a pointer to right child */
struct Node
{
    int data;
    struct Node* left, *right;
};

/* utility that allocates a new node with the
given data and NULL left and right pointers. */
struct Node* newnode(int data)
{
    struct Node* node = new Node;
    node->data = data;
    node->left = node->right  = NULL;
    return (node);
}

// function to check if there exist any subtree with given sum
// cur_sum  --> sum of current subtree from ptr as root
// sum_left --> sum of left subtree from ptr as root
// sum_right --> sum of right subtree from ptr as root
bool sumSubtreeUtil(struct Node *ptr, int *cur_sum, int sum)
{
    // base condition
    if (ptr == NULL)
    {
        *cur_sum = 0;
        return false;
    }

    // Here first we go to left sub-tree, then right subtree
    // then first we calculate sum of all nodes of subtree
    // having ptr as root and assign it as cur_sum
    // cur_sum = sum_left + sum_right + ptr->data
    // after that we check if cur_sum == sum
    int sum_left = 0, sum_right = 0;
    return ( sumSubtreeUtil(ptr->left, &sum_left, sum) ||
             sumSubtreeUtil(ptr->right, &sum_right, sum) ||
        ((*cur_sum = sum_left + sum_right + ptr->data) == sum));
}

// Wrapper over sumSubtreeUtil()
bool sumSubtree(struct Node *root, int sum)
{
    // Initialize sum of subtree with root
    int cur_sum = 0;

    return sumSubtreeUtil(root, &cur_sum, sum);
}

// driver program to run the case
int main()
{
    struct Node *root = newnode(8);
    root->left    = newnode(5);
    root->right   = newnode(4);
    root->left->left = newnode(9);
    root->left->right = newnode(7);
    root->left->right->left = newnode(1);
    root->left->right->right = newnode(12);
    root->left->right->right->right = newnode(2);
    root->right->right = newnode(11);
    root->right->right->left = newnode(3);
    int sum = 22;

    if (sumSubtree(root, sum))
        cout << "Yes";
    else
        cout << "No";
    return 0;
}

Output:

Yes

This article is contributed by Shashank Mishra ( Gullu ). If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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