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

Note:

  1. 3 <= A.length <= 10000
  2. 0 <= A[i] <= 10^6
  3. A is a mountain, as defined above.
    因为山峰的数字肯定是大于左边的数字跟右边的数字,所以用二分查找左右逼近找速度比较快。

     
     1 int peakIndexInMountainArray(int* A, int ASize) {
     2     int low=0,high=ASize,mid;
     3     while(low<high){
     4         mid=low+(high-low)/2;
     5         if(A[mid]>A[mid+1]) high=mid;
     6         else    low=mid+1;
     7         
     8     }
     9     return low;
    10 }

     

posted @ 2018-10-18 23:33  杜王町上班族  阅读(86)  评论(0编辑  收藏  举报