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.

Note: A leaf is a node with no children.

Example:

Given the below binary tree and sum = 22,

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

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

Solution: Recursion

Time complexity: O(n)

Space complexity: O(n)

// Author: Huahua

// Running time: 4 ms

class Solution {

public:

bool hasPathSum(TreeNode* root, int sum) {

if (!root) return false;

if (!root->left && !root->right) return root->val==sum;

int new_sum = sum - root->val;

return hasPathSum(root->left, new_sum) || hasPathSum(root->right, new_sum);

}

};

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