Binary Tree Path Sum

Problem

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

Given the below binary tree and sum = 22,

      5
     / \
    4   8
   /   / \
  11  13  4
 /  \      \
7    2      1

return true, as there exists a root-to-leaf path (5->4->11->2) with a sum of 22.

The binary tree:

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL)}
};

Solution

A depth-first search is being used.

class Solution {
public:
    bool deepFirstSearch(TreeNode *node, int sum, int curSum)
    {
        if (node == NULL) return false;

        if (node->left == NULL && node->right == NULL) {
            return curSum + node->val == sum;
        }

        return deepFirstSearch(node->left, sum, curSum + node->val) || deepFirstSearch(node->right, sum, curSum + node->val);
    }

    bool hasPathSum(TreeNode *root, int sum) {
        return deepFirstSearch(root, sum, 0);
    }
};

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