Unique Binary Search Trees II Leetcode Python

生成唯一BST组合

最新推荐文章于 2025-11-26 15:40:52 发布

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本文介绍了一种算法，用于生成所有可能的独特二叉搜索树（BST），这些树存储从1到给定数字n的值。通过递归地选择根节点并构建左右子树来实现这一目标。

Given n, generate all structurally unique BST's (binary search trees) that store values 1...n.

For example,
Given n = 3, your program should return all 5 unique BST's shown below.

1 3 3 2 1
\ / / / \ \
3 2 1 1 3 2
/ / \ \
2 1 2 3

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

这道题目的做法和之前的unique BST略有不同，但主体思想是一致的。选定一个点作为根，依次产生可行的子树，然后把解加到最后的解里面。

The way to solve this problem is to find a root in the given number then construct valid left and right subtrees then append it to the solution. valid condition is left<mid<right

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

class Solution:
    # @return a list of tree node
    def getTree(self,start,end):
        if start>end:
            return [None]
        solution=[]
        for rootval in range(start,end+1):
            left=self.getTree(start,rootval-1)
            right=self.getTree(rootval+1,end)
            for i in left:
                for j in right:
                    root=TreeNode(rootval)
                    root.left=i
                    root.right=j
                    solution.append(root)
        return solution            
    def generateTrees(self, n):
        return self.getTree(1,n)