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;}
}