算法分析与设计——LeetCode Problem.653 Two Sum IV

题目链接

问题描述

Given a Binary Search Tree and a target number, return true if there exist two elements in the BST such that their sum is equal to the given target.

Example 1:

Input:     5   / \  3   6 / \   \2   4   7Target = 9Output: True

Example 2:

Input:     5   / \  3   6 / \   \2   4   7Target = 28Output: False

解题思路

可以将BST中序遍历一次，这样遍历的数据必是按升序排列，在遍历时将读到的数据存入vector中，然后用夹逼法得出结果即可。

（BST相关问题很多时候需要用到中序遍历）

class Solution {public:bool findTarget(TreeNode* root, int k) {if (root == NULL) {return false;}vector<int> v1;inorder(root, v1);int total = v1.size();int h = 0, t = total - 1;while (1) {if (h == t) return false;if (v1[h] + v1[t] == k) {return true;}if (v1[h] + v1[t] < k) {h++;continue;}if (v1[h] + v1[t] > k) {t--;continue;}}}private:void inorder(TreeNode *r, vector<int> &vec) {if (r != NULL) {inorder(r->left, vec);vec.push_back(r->val);inorder(r->right, vec);}}};