LeetCode95. 不同的二叉搜索樹 II

1、題目描述

https://leetcode-cn.com/problems/unique-binary-search-trees-ii/

給定一個整數 n，生成所有由 1 ... n 爲節點所組成的 二叉搜索樹 。0 <= n <= 8

相關題：96. 不同的二叉搜索樹（多少種） https://blog.csdn.net/IOT_victor/article/details/107066267

2、代碼詳解

遞歸法

# Definition for a binary tree node.
class TreeNode(object):
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right


class Solution(object):
    def generateTrees(self, n):
        """
        :type n: int
        :rtype: List[TreeNode]
        """
        if n == 0:
            return []
        return self.dfs(1, n)

    def dfs(self, start, end):
        if start > end:
            return [None]
        res = []
        for rootval in range(start, end + 1):  # 選一個root
            LeftTree = self.dfs(start, rootval - 1)  # 左子樹所有可能
            RightTree = self.dfs(rootval + 1, end)  # 右子樹所有可能

            # 連接在一起
            for i in LeftTree:
                for j in RightTree:
                    root = TreeNode(rootval)
                    root.left = i
                    root.right = j
                    res.append(root)
        return res

https://leetcode-cn.com/problems/unique-binary-search-trees-ii/solution/bu-tong-de-er-cha-sou-suo-shu-ii-by-leetcode/