HDU - 4135 Co-prime(容斥原理)

#include <iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<vector>
#define ll long long
#define ull unsigned long long
#define LOCAL

using namespace std;
const int maxn=5000+10;
const int inf=0x3f3f3f3f;
const int mod=1e9+7;

vector<ll> v;
ll a,b,n;

void getPrime(ll n){//素数分解，要求的n较少时
    v.clear();
    for(ll i = 2;i*i<=n;i++){
        if(n%i==0){
            v.push_back(i);
            while(n%i==0) n/=i;
        }
    }
    if(n>1) v.push_back(n);
    return ;
}

ll solve(ll x,ll n){
    getPrime(n);
    ll sum=0,val,cnt;
    for(ll i=1;i<(1<<v.size());i++){
        val=1;
        cnt=0;
        for(ll j=0;j<v.size();j++){
            if((1<<j)&i){
                val*=v[j];
                cnt++;
            }
        }
        if(cnt&1) sum+=x/val;
        else sum-=x/val;
    }
    return x-sum;
}

int main(){
    int t;
    scanf("%d",&t);
    for(int i=1;i<=t;i++){

        cin>>a>>b>>n;
        printf("Case #%d: %I64d\n",i,solve(b,n)-solve(a-1,n));
    }
    return 0;
}