hdu1796 How many integers can you find 容斥原理

Now you get a number N, and a M-integers set, you should find out how many integers which are small than N, that they can divided exactly by any integers in the set. For example, N=12, and M-integer set is {2,3}, so there is another set {2,3,4,6,8,9,10}, all the integers of the set can be divided exactly by 2 or 3. As a result, you just output the number 7.

容斥原理裸题

 #include<stdio.h>
 #include<string.h>
 #include<algorithm>
 #include<math.h>
 using namespace std;
 typedef long long ll;
 
 inline int gcd(int a,int b){
     return b?gcd(b,a%b):a;
 }
 
 int num[];
 
 int main(){
     int n,m;
     while(scanf("%d%d",&n,&m)!=EOF){
         n--;
         for(int i=;i<=m;++i){
             scanf("%d",&num[i]);
             if(!num[i]){
                 i--;
                 m--;
             }
         }
         ll ans=;
         for(int i=;i<(<<m);++i){
             int bit=;
             int tmp=;
             for(int j=;j<=m;++j){
                 if(i&(<<(j-))){
                     bit++;
                     tmp=tmp/gcd(tmp,num[j])*num[j];
                 }
             }
             if(bit%)ans+=n/tmp;
             else ans-=n/tmp;
         }
         printf("%lld\n",ans);
     }
     return ;
 }