问N个数中可能的三角形总数

EN

int Search_Closest(A,p,q,n)  /*Returns the index of the element closest to n in array 
                                  A[p..q]*/

{
   if(p<q)
   {
      int r = (p+q)/2;
      if(n==A[r])
         return r;
      if(p==r)
         return r;
      if(n<A[r])
         Search_Closest(A,p,r,n);
      else 
         Search_Closest(A,r,q,n);
   }
   else
      return p;
 }



   int no_of_triangles(A,p,q) /*Returns the no of triangles possible in A[p..q]*/
   {
      int sum = 0;
      Quicksort(A,p,q);  //Sorts the array A[p..q] in O(nlgn) expected case time
      for(int i=p;i<=q;i++)
          for(int j =i+1;j<=q;j++)
           {
               int c = A[i]+A[j];
               int k = Search_Closest(A,j,q,c);
               /* no of triangles formed with A[i] and A[j] as two sides is (k+1)-2 if A[k] is small or equal to c else its (k+1)-3. As index starts from zero we need to add 1 to the value*/
               if(A[k]>c)
                    sum+=k-2;
               else 
                    sum+=k-1;
            }
       return sum;
   }