Ural 1091. Tmutarakan Exams 容斥原理

int c[30][30];
int p[11] = { 2, 3, 5, 7, 11, 13, 17, 19, 23, 29 };
int ans;
int k, s;
void init()
{
for (int i = 1; i <= 29; i++)
{
c[i][0] = c[i][i] = 1;
for (int j = 1; j < i; j++)
c[i][j] = c[i - 1][j - 1] + c[i - 1][j];
}
}
void dfs(int id,int flag,int lcm){
if(id==10)return;
dfs(id+1,flag,lcm);
int lcm1=lcm*p[id];
int l=s/lcm1;
if(l<k)return;//剪支
ans+=c[l][k]*flag;
dfs(id+1,-flag,lcm1);
}
int main(){
init();
while(~sf("%d%d",&k,&s)){
ans=0;
dfs(0,1,1);
if(ans>10000)ans=10000;
pf("%d\n",ans);
}
}