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  • 【leetcode】109. Convert Sorted List to Binary Search Tree

    题目如下:

    Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.

    For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every node never differ by more than 1.

    Example:

    Given the sorted linked list: [-10,-3,0,5,9],
    
    One possible answer is: [0,-3,9,-10,null,5], which represents the following height balanced BST:
    
          0
         / 
       -3   9
       /   /
     -10  5
    
     

    解题思路:题目没有明确要求不允许使用额外的内存,所以最简单的方法是把linked list中每个元素的值存入list,然后套用【leetcode】108. Convert Sorted Array to Binary Search Tree 的解法。

    代码如下:

    # Definition for singly-linked list.
    # class ListNode(object):
    #     def __init__(self, x):
    #         self.val = x
    #         self.next = None
    
    # Definition for a binary tree node.
    # class TreeNode(object):
    #     def __init__(self, x):
    #         self.val = x
    #         self.left = None
    #         self.right = None
    
    class Solution(object):
        def recursive(self,node,nums):
            mid = len(nums)/2
            left_num = nums[:mid]
            if len(left_num) > 0:
                node.left = TreeNode(left_num[len(left_num)/2])
                self.recursive(node.left,left_num)
            right_num = nums[mid+1:]
            if len(right_num) > 0:
                node.right = TreeNode(right_num[len(right_num)/2])
                self.recursive(node.right,right_num)
        def sortedListToBST(self, head):
            """
            :type head: ListNode
            :rtype: TreeNode
            """
            nums = []
            while head != None:
                nums.append(head.val)
                head = head.next
            if len(nums) == 0:
                return None
            root = TreeNode(nums[len(nums)/2])
            self.recursive(root,nums)
            return root
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  • 原文地址:https://www.cnblogs.com/seyjs/p/10625312.html
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