题目

https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/

Given an integer array nums where the elements are sorted in ascending order, convert it to a height-balanced binary search tree.

A height-balanced binary tree is a binary tree in which the depth of the two subtrees of every node never differs by more than one.

Example 1:

Input: nums = [-10,-3,0,5,9]
Output: [0,-3,9,-10,null,5]
Explanation: [0,-10,5,null,-3,null,9] is also accepted:

Example 2:

Input: nums = [1,3]
Output: [3,1]
Explanation: [1,3] and [3,1] are both a height-balanced BSTs.

思路

二叉搜索树：中序遍历生成的数组就是升序排列的

因为 depth of the two subtrees of every node never differs by more than one.高度差不超过1

我们以中间作为根节点，这样能尽量平衡，分成左右俩部分dfs即可

1 2 【3】 4 5

1 2 3 【4】 5 6

代码

class Solution {
public TreeNode sortedArrayToBST(int[] nums) {
if (nums.length==0){
return null;
}
return fun(nums,0,nums.length-1);
}

public TreeNode fun(int\[\] nums,int left,int right){  
    if(left>right)  
        return null;  
    int mid=left+(right-left)/2;//找到根节点  
    TreeNode root=new TreeNode(nums\[mid\]);  
    //分成两个部分，\[left,根节点-1\]\[根节点+1,right\]  
    root.left=fun(nums,left,mid-1);  
    root.right=fun(nums,mid+1,right);

    return root;  
}  

}