108. Convert Sorted Array to Binary Search Tree

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

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

2/17/2017, Java

performance不好

public class Solution {
    public TreeNode sortedArrayToBST(int[] nums) {
        if (nums == null) return null;
        return sortedArrayToBST(nums, 0, nums.length - 1);
    }
    private TreeNode sortedArrayToBST(int[] nums, int lo, int hi) {
        if (lo > hi) return null;
        int mid = lo + (hi - lo) / 2;
        TreeNode ret = new TreeNode(nums[mid]);
        ret.left = sortedArrayToBST(nums, lo, mid - 1);
        ret.right = sortedArrayToBST(nums, mid + 1, hi);
        return ret;
    }
}