2018 912 questions ---- divide and conquer Tsinghua University

Singlet vector is defined as A [0, n), where the prefix {a0, a1, ..., ak} strictly increasing, suffixes {ak + 1, ak + 2, ..., an-1} strictly decreasing. Design algorithm finds the location of the maximum value k in O (logn) time.

int find (int arr[],int len){
   if (len ==1) {
       return 0;
   }
   if (arr[0]<arr[1]) {
       return 0;
   }

   int low = 0,high = len -1;
   if(arr[high ]> arr[high - 1]){
       return high;
   }
   int mid = 0;
   while (low<high) {
       mid = (low+high)/2;
       if (arr[mid]>=arr[mid -1]&&arr[mid] > arr[mid+1]) {
           return mid;
       }
       if (arr[mid] > arr[mid+1]) {
           high = mid -1;
       }
       if (arr[mid] > arr[mid-1]) {
           low = mid + 1;
       }
   }
   return mid;
}