[leetcode] @python Convert Sorted List to Binary Search Tree

crystal_tyan

于 2015-03-11 14:13:16 发布

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分类专栏： OJ 文章标签： bst

本文链接：https://blog.youkuaiyun.com/crystal_tyan/article/details/44198151

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本文探讨了如何自底向上构建二叉搜索树(BST)，并介绍了将单链表转换为BST的方法，包括定义节点类和构建BST的过程。

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好像可以自底向上构造BST吧，不过我是转成array做的

# Definition for a  binary tree node
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#
# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    # @param head, a list node
    # @return a tree node
    def sortedListToBST(self, head):
        if head is None: return None
        array = self.toArray(head)
        return self.buildBST(array, 0, len(array)-1)

    def buildBST(self, array, left, right):
        if left > right: return None
        mid = (left + right) / 2
        root = TreeNode(array[mid])
        root.left = self.buildBST(array, left, mid-1)
        root.right = self.buildBST(array, mid+1, right)
        return root

    def toArray(self, head):
        rst = []
        while head is not None:
            rst.append(head.val)
            head = head.next
        return rst