[LeetCode] 669.Trim a Binary Search Tree

• 题目描述
• 解题思路
• 实验代码

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题目描述

Given a binary search tree and the lowest and highest boundaries as L and R, trim the tree so that all its elements lies in [L, R] (R >= L). You might need to change the root of the tree, so the result should return the new root of the trimmed binary search tree.

Example 1:

Input:
　 　1
　/ 　\
0 　　 2

L = 1
R = 2

Output:
　 1
　　 \
　　 2

Example ２:

Input:
　 　 3
　 /　 \
　 0 　4
　 \
　 2
　 /
　1

L = 1
R = ３

Output:
　　　3
　 　 /
　 　2
　 /
　 1

解题思路

一道很简单的关于二叉搜索树的题目，解决这道题目的关键是明确二叉搜索树的概念，知道根节点和左右子节点之间的关系。判断L和R与节点的值的大小时出现的情况要想清楚，同时做出正确的递归。具体见代码。

实验代码

/** * 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:    TreeNode* trimBST(TreeNode* root, int L, int R) {        if (root == NULL) return NULL;        if (root->val < L) return trimBST(root->right, L, R);        if (root->val > R) return trimBST(root->left, L, R);        root->left = trimBST(root->left, L, R);        root->right = trimBST(root->right, L, R);        return root;    }};