[每日 LeetCode] 112. Path Sum

原文链接 [每日 LeetCode] 112. Path Sum

Description:

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.

Note: A leaf is a node with no children.

Example:

Given the below binary tree and sum = 22,

      **5**
       /   \
    **4**   8
     /     / \
  **11**   3  4
 /     \       \
7    **2**      1

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

思路：本题要求判断树中是否存在某个和为 sum 的路径，有则返回 true，否则返回 false。依旧使用递归思想，如果当前结点没有子结点，比较当前结点的值和 sum 值，如果当前结点存在子结点，比较当前结点的子结点值是否等于 sum-当前结点值，依次从左到右进行比较。

C++ 代码

/**
 * 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;
        return hasPathSum(root->left, sum - root->val) 
            || hasPathSum(root->right, sum - root->val);
    }
};

运行时间：16ms

运行内存：20.1M