95.不同的二叉搜索树-ii.py

#
# @lc app=LeetCode.cn id=95 lang=python3
#
# [95] 不同的二叉搜索树 II
#

# @lc code=start
# 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):
        def generate(first, last):
            trees = []
            for root in range(first, last+1):
                for left in generate(first, root-1):
                    for right in generate(root+1, last):
                        node = TreeNode(root)
                        node.left = left
                        node.right = right
                        trees += [node]
            return trees or [None]
        return generate(1, n)
    


# @lc code=end