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：这道题是典型的dfs搜索路径的问题，每次判断根节点是否等于差值，左子树不行就回溯看右子树怎么样。

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    bool hasPathSum(TreeNode* root, int sum) {        if(!root) return false;        if(!root->left&&!root->right)            return sum==root->val;        return hasPathSum(root->left,sum-root->val)||hasPathSum(root->right,sum-root->val);    }};