Solution.java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    private int[] nums;

    public TreeNode sortedArrayToBST(int[] nums) {
        this.nums = nums;
        return dfs(0, nums.length - 1);
    }

    private TreeNode dfs(int i, int j) {
        if (i > j) {
            return null;
        }
        if (i == j) {
            return new TreeNode(nums[i]);
        }
        int mid = (i + j) >>> 1;
        TreeNode node = new TreeNode(nums[mid]);
        node.left = dfs(i, mid - 1);
        node.right = dfs(mid + 1, j);
        return node;
    }
}