112. Path Sum

题意： 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.

思路：直接递归求解就好了。

/** * Definition for a binary tree node. * 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) {        if (root == NULL)            return false;        if(sum == root->val && root->left == NULL && root->right == NULL)            return true;        return hasPathSum(root->left, sum-root->val)||hasPathSum(root->right, sum-root->val);    }};