MERGESORT

void Mergesort(int *a, int l, int r ,int *b, bool (*cmp)(int,int))
{
    int i,j,k,m;
    if (r-l>0)
    {
        m=(r+l)/2;
        Mergesort(a,l,m,b,cmp);
        Mergesort(a,m+1,r,b,cmp);
        for(i=m; i>=l;i--) *(b+i)=*(a+i);
        FOR(j,m+1,r) *(b+r+m+1-j)=*(a+j);
        //cout<<endl;
        //FOR(k,1,n) cout<<b[k]<<" ";
        //cout<<endl;
        //cout<<i<<" "<<j<<" "<<l<<" "<<r<<endl;
        //cout<<endl;
        i++;
        j--;
        FOR(k,l,r)
         if (cmp(*(b+i),*(b+j)))
            {*(a+k)=*(b+i); i++;
           // cout<<k<<" "<<a[k]<<endl;
           }
            else
            {*(a+k)=*(b+j); j--;
           // cout<<k<<" "<<a[k]<<endl;
            }
    }
    return;
}