669. Trim a Binary Search Tree

669. Trim a Binary Search Tree (Easy)

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

Companies:
Microsoft

Related Topics:
Tree

Solution 1.

// OJ: https://leetcode.com/problems/trim-a-binary-search-tree/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(logN)
class Solution {
public:
    TreeNode* trimBST(TreeNode* root, int L, int R) {
        if (!root) 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;
    }
};