Convert Sorted Array to Binary Search Tree

Description

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.

Method

1.将字符串的中间值设为头结点并返回这个头结点。

2.对中间值左边的数组重复1的操作，并作为头结点的左节点返回。

3.对中间值右边的数组重复1的操作，并作为头结点的右节点返回。

Solution

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode sortedArrayToBST(int[] nums) {
        if(nums.length == 0) return null;
        return makeTree(nums, 0, nums.length - 1);
    }
    
    public TreeNode makeTree(int[] nums, int start, int end){
        if(end < start) return null;
        int mid = start + (end - start)/2;
        TreeNode node = new TreeNode(nums[mid]);
        node.right = makeTree(nums, mid + 1, end);
        node.left = makeTree(nums, start, mid - 1);
        return node;
    }
}