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

解题要点：

找到数组里最大值，拿这个值和它的后一位比较，大于就返回这个数。

class Solution {
    public int peakIndexInMountainArray(int[] A) {
        int max = -1;
        for(int i = 0; i < A.length - 1; i++){
            if(max < A[i]) max = A[i];
            if(max > A[i + 1]) return i;
        }
        return 0;
    }
}