HDU 1796 How many integers can you find(容斥原理）

 1 #include<iostream>
 2 #include<cstring>
 3 #include<cstdio>
 4 #include<cmath>
 5 #include<algorithm>
 6 using namespace std;
 7 const long long N=205;
 8 long long a[N],n,m,ans;
 9 long long gcd(long long x,long long y){
10     if(y==0)return x;
11     else return gcd(y,x%y);
12 }
13 long long lcm(long long x,long long y){
14     return x/gcd(x,y)*y;
15 }
16 void dfs(long long now,long long num,long long res,long long k){
17     if(res==0){
18         if(num==0)return;
19         long long tmp=n/num;
20         if(k&1)ans+=tmp;
21         else ans-=tmp;
22         return;
23     }
24     if(now==m+1)return ;
25     if(lcm(num,a[now])<=n)dfs(now+1,lcm(num,a[now]),res-1,k);
26     dfs(now+1,num,res,k);
27 }
28 int main(){
29     while(scanf("%lld%lld",&n,&m)!=EOF){
30         n--;
31         for(long long i=1;i<=m;i++)scanf("%lld",&a[i]);
32         for(long long i=1;i<=m;i++)dfs(1,1,i,i);
33         printf("%lld\n",ans);
34     }
35 }