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.

class Solution {
public:
    bool hasPathSum(TreeNode *root, int sum) {
        if(root == NULL)//当输入为{}, 0时需要输出false
        {
        	return false;
        }
        sum -= root->val;
        if(root->left == NULL && root->right == NULL && sum == 0)//题目要求搜索要终止于叶结点
        {
        	return true;
        }
        else
        {
        	return hasPathSum(root->left, sum) || hasPathSum(root->right, sum);
        }
    }
};