Description
Given an integer n, return all the structurally unique BST's (binary search trees), which has exactly n nodes of unique values from 1 to n. Return the answer in any order.
Example 1:
Input: n = 3 Output: [[1,null,2,null,3],[1,null,3,2],[2,1,3],[3,1,null,null,2],[3,2,null,1]]
Example 2:
Input: n = 1 Output: [[1]]
Constraints:
1 <= n <= 8
Solution
Python3
# 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 generateTrees(self, n: int) -> List[Optional[TreeNode]]:
def generate(start, end):
if start > end:
return [None]
res = []
for mid in range(start, end + 1):
for left in generate(start, mid - 1):
for right in generate(mid + 1, end):
node = TreeNode(mid, left, right)
res.append(node)
return res
return generate(1, n)