LeetCode - Convert Sorted Array to Binary Search Tree

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

题目需要构建height-balanced BST, 应该能想到找到中间的点，然后构造，构造的时候用DFS

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public TreeNode sortedArrayToBST(int[] nums) {
        if (nums == null || nums.length == 0) {
            return null;
        }
        return buildTree(0, nums.length-1, nums);
    }

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