162.Find-Peak-Element

162. Find Peak Element

题目地址

http://www.lintcode.com/problem/find-peak-element/

http://www.jiuzhang.com/solutions/find-peak-element/

题目描述

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 peak if:

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

代码

public class Solution {

  int start = 1, end = A.length - 2;
  while (start + 1 < end) {
    int mid = (start + end) / 2;
    if (A[mid] < A[mid - 1]) {
      end = mid;
    } else if (A[mid] < A[mid + 1] ) {
            start = mid;
    } else {
      end = mid;
    }
  }

  if (A[start] < A[end]) {
    return end;
  } else {
    return start;
  }

}