leetcode刷题，总结，记录，备忘 112

leetcode112Path 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.
使用递归，只有在叶节点的时候才真正的计算是否相等，然后将结果返回出去，其余父节点处只需得到2个分支的结果的或结果即可。
/**
* 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 Has(TreeNode * root, int sum, int result)
{
if (root == NULL)
{
return false;
}

if (root->left == NULL && root->right == NULL)
{
return root->val + result == sum;
}

return Has(root->left, sum, result + root->val) || Has(root->right, sum, result + root->val);

}

bool hasPathSum(TreeNode* root, int sum) {
return Has(root, sum, 0);
}
};