Path sum(C++ code)

Leetcode 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.
思路：递归。要注意的是valid path必须是从root到leaf,如果只有一边没有孩子 ，是不算叶子的。。

1. bool hasPathSum(TreeNode *root, int sum) {  
2.         if(!root) return false;  
3.         int update = sum - root->val;  
4.         if(!root->left && !root->right) return (update == 0)? true : false;  
5.         return hasPathSum(root->left, update)  ||  hasPathSum(root->right, update);  
6.     }