//二分搜索
   //时间复杂度小 log2 n

 int search(int key, int a[], int len)

 {

     int ret = -;

     int left = ;

     int right = len-;

     int mid;

     while(left<right)

     {

         mid = (right + left)/;

         if(a[mid] == key)

         {

             ret = mid;

             break;

         }else if(a[mid] >key){

             right  = mid-;

         }else{

             left = mid-;

         }

     }

     return ret;

 }

 int main()

 {

     int a[] = {,,,,};

     int r = search(, a, sizeof(a)/sizeof(a[]));

     printf("%d",r);

     return ;

 }