Q: 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.

A： 深度搜索。注意节点的val值有正有负，原先以为节点值都为正数，做了个剪枝：root->val>sum.

bool hasPathSum(TreeNode *root, int sum) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if(root==NULL)            return false;                if(root->val==sum&&!root->left&&!root->right)            return true;        else            return hasPathSum(root->left,sum-root->val)||hasPathSum(root->right,sum-root->val);            }