hdu4135 Co-prime 容斥原理

Given a number N, you are asked to count the number of integers between A and B inclusive which are relatively prime to N.
Two integers are said to be co-prime or relatively prime if they have no common positive divisors other than 1 or, equivalently, if their greatest common divisor is 1. The number 1 is relatively prime to every integer.

容斥原理

 #include<stdio.h>
 #include<string.h>
 #include<algorithm>
 #include<math.h>
 using namespace std;
 typedef long long ll;

 int pnum[];

 int main(){
     int T;
     scanf("%d",&T);
     for(int q=;q<=T;++q){
         ll a,b;
         int n;
         scanf("%lld%lld%d",&a,&b,&n);
         a--;
         ll ans=;
         int cnt=;
         for(int i=;i*(ll)i<=n;++i){
             if(!(n%i)){
                 pnum[++cnt]=i;
                 while(!(n%i))n/=i;
             }
         }
         if(n>)pnum[++cnt]=n;
         for(int i=;i<(<<cnt);++i){
             int bit=;
             int mul=;
             for(int j=;j<=cnt;++j){
                 if(i&(<<(j-))){
                     bit++;
                     mul*=pnum[j];
                 }
             }
             if(bit%)ans+=b/mul-a/mul;
             else ans-=b/mul-a/mul;
         }
         printf("Case #%d: %lld\n",q,b-a-ans);
     }
     return ;
 }