[LeetCode]Path Sum

题目解析:(链接)

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.

解题思路：

深度优先搜索

 1 /**
 2  * Definition for a binary tree node.
 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 dfs(TreeNode *root, int sum, int cur_sum) {
13         if (!root) {
14             return false;
15         }
16         
17         if (root->left == nullptr && root->right == nullptr) {
18             return sum == cur_sum + root->val;
19         }
20         
21         return dfs(root->left, sum, cur_sum + root->val) || dfs(root->right, sum, cur_sum + root->val);
22     }
23     
24     bool hasPathSum(TreeNode* root, int sum) {
25         return dfs(root, sum, 0);
26     }
27 };