[leetcode] 112.Path Sum

题目：

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.

题意：

给定一棵树，查找是否存在从根节点到叶子节点的一个路径，路径上元素之和等于一个给定值。

思路：

采用递归的思路进行解决，将给定值减去当前根节点的值，然后作为给定值递归左子树跟右子树。

以上。

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 hasPathSum(TreeNode* root, int sum) {
if(root == NULL)return false;
return PathSum(root, sum);
}
bool PathSum(TreeNode* root, int sum) {
if(root->left == NULL && root->right == NULL){
if(root->val != sum)return false;
else return true;
}
else if(root->left != NULL && PathSum(root->left,sum - root->val))return true;
else if(root->right != NULL && PathSum(root->right,sum - root->val))return true;
else return false;
}
};