【Leetcode】【python】Unique Binary Search Trees II

题目大意

给出一个n，求1-n能够得到的所有二叉搜索树，输出所有树

解题思路

该题较难，参考题解的思路。

我自己的理解就是从start到end，先把左右字数的所有可能先迭代出来，之后递归加入左右字数，生成每一颗新树。

代码

class Solution(object):    def generateTrees(self, n):        if n == 0:            return []        return self.helper(1, n)    def helper(self, start, end):        result = []        if start > end:            result.append(None)            return result        for i in range(start, end + 1):            # generate left and right sub tree            leftTree = self.helper(start, i - 1)            rightTree = self.helper(i + 1, end)            # link left and right sub tree to root(i)            for j in range(len(leftTree)):                for k in range(len(rightTree)):                    root = TreeNode(i)                    root.left = leftTree[j]                    root.right = rightTree[k]                    result.append(root)        return result

总结