LeetCode-Java-852. Peak Index in a Mountain Array

题目

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
Note:

3 <= A.length <= 10000
0 <= A[i] <= 10^6
A is a mountain, as defined above.

代码

主要是运用了二分的原理

class Solution {
    public int peakIndexInMountainArray(int[] A) {
        int len = A.length;
        int s = 0;
        int e = len-1;
        int mid=0;
        while(s<e)
        {
            mid = (s+e)>>>1;
            if(A[mid]>A[mid-1]&&A[mid]>A[mid+1])
                break;
            else if(A[mid]>A[mid-1])
            {
                s = mid;
            }
            else if(A[mid]<A[mid-1])
            {
                e = mid;
            }
        }
        return mid;
    }
}