trim-a-binary-search-tree

Trim a Binary Search Tree – LeetCode 669

Problem

Description

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.

Answer

Original

Code

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/**
* 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){
if(root->val < L)
return trimBST(root->right, L, R);
else if(R < root->val)
return trimBST(root->left, L, R);
else {
root->left = trimBST(root->left, L, R);
root->right = trimBST(root->right, L, R);
return root;
}
} else
return nullptr;
}
};

思路

简单的DFS删除,注意维护返回的根节点。时间复杂度$O(n)$,空间复杂度$O(n)$。
耗时$8$ ms,排名$1.46\%$

Better

思路

还没看到更好的思路