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.

For 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.

 

水！

 

1 /** 2  * Definition for binary tree 3  * struct TreeNode { 4  *     int val; 5  *     TreeNode *left; 6  *     TreeNode *right; 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8  * }; 9  */10 class Solution {11 public:12     bool hasPathSum(TreeNode *root, int sum) {13         if (root == NULL) {14             return false;15         }16         if (root->left == NULL && root->right == NULL) {17             return root->val == sum;18         }19         bool flag1 = hasPathSum(root->left, sum - root->val);20         bool flag2 = hasPathSum(root->right, sum - root->val);21         return flag1 || flag2;22     }23 };