[LeetCode] Path Sum

Path Sum:

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.

注意用sum剪枝的前提是所有节点的值都正。

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    bool hasPathSum(TreeNode *root, int sum) {        // Start typing your C/C++ solution below        // DO NOT write int main() function            if ( !root  )return false; if ( !root->left && !root->right )return root->val==sum;return hasPathSum(root->left,sum-root->val)|| hasPathSum(root->right,sum-root->val);    }};