LC 0669 [M] Trim a Binary Search Tree - ALawliet/algorithms GitHub Wiki

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def trimBST(self, root: Optional[TreeNode], low: int, high: int) -> Optional[TreeNode]:
        if not root:
            return None
        
        if root.val > high: # we can throw out the entire right subtree
            return self.trimBST(root.left, low, high)
        if root.val < low: # we can throw out the entire left subtree
            return self.trimBST(root.right, low, high)
        
        # the subtree is in bounds but its subtrees may not be so we may have to trim and reassign
        root.left = self.trimBST(root.left, low, high)
        root.right = self.trimBST(root.right, low, high)

        return root