LeetCode——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.

给一个升序有序的数组，构建一个平衡的二叉查找树。

要平衡就要找中间的数来做头结点，递归构造。

/**
 * 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;
        }

        TreeNode root = createBST(nums, 0, nums.length-1);

        return root;
    }

    public TreeNode createBST(int[] nums, int left, int right) {
        if(left > right) {
            return null;
        }
        int mid = (left + right) / 2;
        TreeNode node = new TreeNode(nums[mid]);
        node.left = createBST(nums, left, mid-1);
        node.right = createBST(nums, mid+1, right);

        return node;
    }
}