README.md

669. Trim a Binary Search Tree

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

Solutions (Python)

1. Recursion

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    def trimBST(self, root: TreeNode, L: int, R: int) -> TreeNode:
        if not root:
            return root
        elif root.val > R:
            return self.trimBST(root.left, L, R)
        elif root.val < L:
            return self.trimBST(root.right, L, R)
        else:
            root.left = self.trimBST(root.left, L, R)
            root.right = self.trimBST(root.right, L, R)
            return root