Find Peak Element

There is an integer array which has the following features:

The numbers in adjacent positions are different. A[0] < A[1] && A[A.length - 2] > A[A.length - 1]. We define a position P is a peek if:

A[P] > A[P-1] && A[P] > A[P+1] Find a peak element in this array. Return the index of the peak.

Example:

Given [1, 2, 1, 3, 4, 5, 7, 6]

Return index 1 (which is number 2) or 6 (which is number 7)

Notes:

1. The condition make sure the question has at least one solution
2. Method 1: loop to compare with the adjacent items O(n) time
3. Method 2: Binary search, keep half. The solution must not exist in the half which could not meet the condition.

    public int findPeak(int[] nums) {
        if (nums == null || nums.length <= 2) {
            return -1;
        }

        int start = 1;
        int end = nums.length-2;

        while(start+1 < end) {
            int mid = start + (end-start)/2;

            if (nums[mid] < nums[mid+1]) {
                start = mid;
            } else if (nums[mid] < nums[mid-1]) {
                end = mid;
            } else {
                return mid;
            }
        }

        if (nums[start] > nums[end]) {
            return start;
        }

        return end;
    }