852. Peak Index in a Mountain Array

Let's call an array A a mountain if the following properties hold:

• A.length >= 3
• There exists some 0 < i < A.length - 1 such that A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1]

Given an array that is definitely a mountain, return any i such that A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1].

Example 1:

Input: [0,1,0]
Output: 1

Example 2:

Input: [0,2,1,0]
Output: 1

分析： binary search

class Solution {
    public int peakIndexInMountainArray(int[] A) {
        int start = 0, end = A.length - 1;
        while (start < end) {
            int mid = start + (end - start) / 2;
            if (A[mid] < A[mid + 1]) {
                start = mid + 1;
            } else {
                end = mid;
            }
        }
        return start;
    }
}