LeetCode (12) Path Sum (二叉树路径和判断)

题目描述

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,

return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

因此，本题要求判断二叉树某一条路径的和是否为给定的数值。本题的思路为深度优先搜索。

/**
 * 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)
        {
            return false;
        }

        if (!root->left && !root->right && root->val == sum)
            return true;

        if (hasPathSum(root->left, sum-root->val))
            return true;
        else if (hasPathSum(root->right, sum-root->val))
            return true;
        else
            return false;
    }
};