Thinking process

The given two conditions imply there must be a peak.

Discuss different cases

• if it is the peak, then return
• if the left is smaller than current, then move start position to curr
• if the right is smaller than current, then move end position to curr

Mistakes

if length of A is 1, return 0;

if length of A is 2, return the largest;

class Solution {
    /**
     * @param A: An integers array.
     * @return: return any of peek positions.
     */
    public int findPeak(int[] A) {
        // write your code here

        if (A == null || A.length <= 2) {
            return 0;
        }

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

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

            if (A[mid] > A[mid - 1] && A[mid] > A[mid + 1]) {
                return mid;
            } else if (A[mid] > A[mid - 1]) {
                start = mid;
            } else {
                end = mid;
            }
        }

        return A[start] > A[end] ? start : end;
    }
}