return the index of that peek or valey

给定一个array,条件：1. A[i] = A[i-1]+-1; 2. There is only one peek or one valey in the array, return the index of that peek or valey.

public static int find(int[] nums) {if (nums.length == 0)return -1;int len = nums.length;if (Math.abs(nums[len - 1] - nums[0]) == len - 1)return -1;// There is no such a valley or peakreturn helper(nums, 0, len - 1);}public static int helper(int[] nums, int start, int end) {int mid = start + (end - start) / 2;if ((nums[mid - 1] - nums[mid]) * (nums[mid + 1] - nums[mid]) > 0)return nums[mid];int diffOfIndex = mid - start;int diffOfValue = Math.abs(nums[mid] - nums[start]);if (diffOfIndex == diffOfValue)start = mid;elseend = mid;return helper(nums, start, end);}public static void main(String[] args) {int[] nums1 = { 1, 2, 3, 4, 3, 2 };int[] nums2 = {};int[] nums3 = { 1, 2, 3, 4, 5, 6, 7, 8, 7 };int[] nums4 = { 1, 2, 3, 4, 5 };int[] nums5 = { 5, 4, 3, 2, 1, 2, 3 };int[] nums6 = { 9, 8, 7, 6, 7 };System.out.println(find(nums1));System.out.println(find(nums2));System.out.println(find(nums3));System.out.println(find(nums4));System.out.println(find(nums5));System.out.println(find(nums6));}