ZROI#997

ZROI#997
这是某场(CF(Div.3))的(C)题.我当时是选择了现场码.
因为那场(CF)我没打.这个题我当时第一眼就觉得有循环节.
于是就直接考虑循环节,发现它是对的.于是就只需要处理一下细节就好.
(Code:)

#include <algorithm>
#include <iostream>
#include <cstdlib>
#include <cstring>
#include <cstdio>
#include <string>
#include <vector>
#include <queue>
#include <cmath>
#include <ctime>
#include <map>
#include <set>
#define MEM(x,y) memset ( x , y , sizeof ( x ) )
#define rep(i,a,b) for (int i = a ; i <= b ; ++ i)
#define per(i,a,b) for (int i = a ; i >= b ; -- i)
#define pii pair < int , int >
#define X first
#define Y second
#define rint read<int>
#define int long long
#define pb push_back

using std::set ;
using std::pair ;
using std::max ;
using std::min ;
using std::priority_queue ;
using std::vector ;
using std::swap ;
using std::sort ;
using std::unique ;
using std::greater ;

template < class T >
    inline T read () {
        T x = 0 , f = 1 ; char ch = getchar () ;
        while ( ch < '0' || ch > '9' ) {
            if ( ch == '-' ) f = - 1 ;
            ch = getchar () ;
        }
       while ( ch >= '0' && ch <= '9' ) {
            x = ( x << 3 ) + ( x << 1 ) + ( ch - 48 ) ;
            ch = getchar () ;
       }
   return f * x ;
}

const int N = 100 ; bool mk[15] ;
int n , m , T , tot ;
vector < int > tmp ;

signed main (int argc , char * argv[]) {
    T = rint () ;
    while ( T -- ) {
        n = rint () ; m = rint () ; tot = 0 ; int sum = 0 ;
        if ( m > n ) { puts ("0") ; continue ; }
        if ( n == m ) { printf ("%lld
" , m % 10 ) ; continue ; }
        rep ( i , 0 , 10 ) mk[i] = false ; tmp.clear () ;
        while ( true ) {
            ++ tot ; int t = m * tot % 10 ; if ( mk[t] ) break ;
            tmp.pb ( t ) ; sum += t ; mk[t] = true ;
        }
        int rpt = ( n / m ) / (int)tmp.size () ; int ans = sum * rpt ;
        rep ( i , 0 , n / m % (int)tmp.size () - 1 ) ans += tmp[i] ;
        printf ("%lld
" , ans ) ;
    }
    return 0 ;
}