【Lintcode】075.Find Peak Element

题目：

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)

题解：

class Solution {
public:
    /**
     * @param A: An integers array.
     * @return: return any of peek positions.
     */
    int findPeak(vector<int> A) {
        if (A.size() < ) {
            return -;
        }

        int n = A.size();
        int start = ;
        int end = n - ;
        while (start < end - ) {
            int mid = start + (end - start) / ;
            if (A[mid] > A[mid - ] && A[mid] > A[mid + ]) {
                return mid;
            } else if (A[mid] > A[mid-]) {
                start = mid;
            } else {
                end = mid;
            }
        }

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

        return -;
    }
};