LeetCode 112: Path Sum

Question:

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.
分析：
题目要求在树中找到一条总和等于Sum的路径，等价于在树的左右两个子树中找到和等于sum-root的路径，这样依次递归。

代码如下：

/**
 * Definition for binary tree
 * 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)
	<span style="white-space:pre">	</span>return false;
	if(root->left ==NULL && root->right==NULL)
		return sum == root->val;
	if (root->left && hasPathSum(root->left, sum-root->val))
		return true;
	if (root->right && hasPathSum(root->right, sum-root->val))
		return true;
	return false;
    }
};