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.

Notice

The array may contains multiple peeks, find any of them.

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

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

Solution: Since it must has such an element. We can do a binary search.

public int findPeak(int[] A) {
    if(A == null || A.length == 0) {
        return -1;
    }
    int start = 0, end = A.length - 1;
    while(start <= end) {
        int mid = start + (end - start) / 2;
        if(A[mid] > A[mid - 1] && A[mid] > A[mid + 1]) {
            return mid;
        }
        else if(A[mid] < A[mid + 1]) {
            start = mid + 1;
        }
        else {
            end = mid - 1;
        }
    }
    return start;
}