原题如下
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. 给定一棵二叉树和sum，判断是否存在这样的一条从根到叶子的路径，它的路径上的值的总和等于sum。 Note: A leaf is a node with no children.
Example:
Given the below binary tree and sum = 22,
代码语言：javascript复制 5
/
4 8
/ /
11 13 4
/
7 2 1return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.
思路
要判断是否存在这样的路径，需要判断其左右子树是否存在总值和为 (sum - root->val)的路径，这样就把问题拆为了子问题，可以不断递归下去。
代码
代码语言：javascript复制/**
* 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;
if(root->left == NULL && root->right == NULL) return root->val == sum;
return hasPathSum(root->left, sum - root->val)
|| hasPathSum(root->right, sum - root->val);
}
};
