[面试真题] 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.

解法：递归方法。

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     bool hasPathSum(TreeNode *root, int sum) {
13         // Start typing your C/C++ solution below
14         // DO NOT write int main() function
15         if(NULL == root){
16             return false;
17         }
18         if(root->val == sum){
19             if(!root->left && !root->right){
20                 return true;
21             }
22             return (hasPathSum(root->left, sum - root->val) || hasPathSum(root->right, sum - root->val));
23         }
24         return (hasPathSum(root->left, sum - root->val) || hasPathSum(root->right, sum - root->val));
25     }
26 };

Run Status: Accepted!

Program Runtime: 60 milli secs

Progress: 114/114 test cases passed.