Reverse number template

逆序对：a[i]>a[j]&&i<j

Adjacent bubble sort number for the number of times the sequence is switched to the reverse

One:

By merge sort

Long  Long   CNT = 0 ;
 void Merge ( int L, int R & lt) 
{ 
    IF (L> = R & lt) return ;
     int MID = (L + R & lt) >> . 1 ; 
    Merge (L, MID), Merge (MID + . 1 , R & lt);
     int I = L, J = MID + . 1 , K = 0 ;
    the while (I <= MID && J <= R & lt)
     IF (A [I] <= A [J]) B [K ++] = A [I ++ ];
    the else B [K ++] = a [J ++], CNT + = MID-I + . 1 ; // when a [i]> a [j ] i <j and i ~ mid j ~ r is a sequence of two ordered, then a [i ~ mid] may be configured to reverse the A [J]
    the while(i<=mid)b[k++]=a[i++];
   while(j<=r)b[k++]=a[j++];
   for(int i=0,j=l;j<=r;j++,i++)
    a[j]=b[i];
   return ;
}

two;

By Fenwick tree