Leetcode 112. Path Sum

求路径和，仅需要一直减去当前节点的数字，然后看看在根结点的时候是否为0，如果不是返回false就行啦

/**
 * 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) return false;
        if(!root->left && !root->right) return sum - root->val == 0;
        return hasPathSum(root->left, sum - root->val) || hasPathSum(root->right, sum - root->val);
    }
};