[leetcode] 112. Path Sum 解题报告

题目链接：https://leetcode.com/problems/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：前序遍历二叉树，到一个节点为叶子节点时判断路径和是否等于给定的值。

代码如下：

/**
* 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 DFS(TreeNode* root, int sum, int curSum)
{
if(root == NULL)    return false;
if(curSum + root->val == sum && !root->left && !root->right)
return true;
return DFS(root->left, sum, curSum + root->val) || DFS(root->right, sum, curSum+root->val);
}
bool hasPathSum(TreeNode* root, int sum) {
return DFS(root, sum, 0);
}
};