lc108. Convert Sorted Array to Binary Search Tree

108. Convert Sorted Array to Binary Search Tree Easy

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Share Given an array 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 array: [-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

思路： BST满足left.key<parent.key<=right.key，所以，数组取中间值，中间值为root，左右子数组做迭代，

代码：python3

class Solution:
    def sortedArrayToBST(self, nums: List[int]) -> TreeNode:
        def convert(left,right):
            if left>right:return None
            mid=(left+right)//2
            node=TreeNode(nums[mid])
            node.left=convert(left,mid-1)
            node.right=convert(mid+1,right)
            return node
        return convert(0,len(nums)-1)

tips:

BST任何一颗子树上的三个节点left, parent, right. 满足条件left.key<parent.key<=right.key，一颗典型的BST如下图所示：