2014 Super Training #3 H Tmutarakan Exams --容斥原理

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
#define ll long long
using namespace std;
#define N 10007

ll C[55][55];
int prime[10] = {2,3,5,7,11,13,17,19,23};

void calc_C()
{
    memset(C,0,sizeof(C));
    C[1][0] = C[1][1] = 1;
    for(int i=2;i<=51;i++)
    {
        C[i][0] = 1;
        for(int j=1;j<=51;j++)
            C[i][j] = C[i-1][j] + C[i-1][j-1];
    }
}

int main()
{
    int k,S,i,j,res,num,flag;
    calc_C();
    while(scanf("%d%d",&k,&S)!=EOF)
    {
        ll res = 0;
        flag = 9;
        for(i=0;i<9;i++)
        {
            num = S/prime[i];
            if(num < k)
            {
                flag = i;
                break;
            }
            else
                res += C[num][k];
        }
        for(i=0;i<flag;i++)
        {
            for(j=i+1;j<flag;j++)
            {
                num = S/(prime[i]*prime[j]);
                if(num < k)
                    break;
                else
                    res -= C[num][k];
            }
        }
        printf("%lld\n",min((ll)10000,res));
    }
    return 0;
}