[Lintcode] Find Peak Element to find the peaks of an array

There is a integer array which has the following features:

• The numbers in adjacent positions is 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 the this array. Return the index of the peak.

Notice

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

Has you met this question in a real interview? Example

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

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

Challenge

Time complexity O (LOGN)

For the original question on Leetcode, please see my previous blog find Peak Element.

Solution One:

classSolution { Public:    /** * @param a:an integers array.     * @return: Return any of peek positions. */    intFindpeak (vector<int>A) {intleft =0, right = A.size ()-1;  while(Left <Right ) {            intMid = left + (right-left)/2; if(A[mid] < A[mid +1]) left = mid +1; Elseright =mid; }        returnRight ; }};

Solution Two:

classSolution { Public:    /** * @param a:an integers array.     * @return: Return any of peek positions. */    intFindpeak (vector<int>A) { for(inti =1; I < a.size (); ++i) {if(A[i] < a[i-1])returnI1; }        returnA.size ()-1; }};

[Lintcode] Find Peak Element to find the peaks of an array