hdu 3501 筛素数 + 容斥模板

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<string>
#define mod 1000000007ll
#define LL long long
using namespace std;
// 筛素数
bool flag[50000];
int cnt = 0,prime[50000];
void Prime(){
    for(LL i=2; i * i <= 1500000000ll; i++){
        if(flag[i])
            continue;
        prime[cnt++] = i;
        for(LL j = i * i; j * j <= 1500000000ll; j += i)
            flag[j]=true;
    }
}
//容斥
LL x[5000], len, n, ans;
void dfs(LL pre, LL index, LL am)
{
    // printf("%I64d %I64d %I64d\n", ans, pre);
     if(am >= 1)
     {
        LL am1 = n / pre;
        if(n % am1 == 0) am1--;
        LL tmp = (pre + pre * am1) * am1 / 2 % mod;
        if(am & 1) ans += tmp;
        else ans -= tmp;
        ans = (ans % mod + mod) % mod;
     }
   //  printf("%I64d\n", ans);
     for(int i = index; i < len; i++)
         dfs(pre * x[i], i + 1, am + 1);
}
// 调试
void debug()
{
     for(int i = 0; i < cnt; i++) if(prime[i]==0)printf("%d\n", prime[i]);
}
int main()
{
    Prime();
   // debug();
    while(scanf("%I64d", &n)!=EOF)
    {
        if(n == 0) break;
        len = 0;
        LL n1 = n;
        for(int i = 0; i < cnt && prime[i] <= n1; i++)
        {
            if(n1%prime[i] == 0)
            {
               x[len++] = prime[i];
               while(n1 % prime[i] == 0) n1 /= prime[i];
            }
        }
       // debug();
        if(n1!=1)x[len++] = n1;
        ans = 0;
        dfs(1, 0, 0);
        printf("%I64d\n", ans);
    }
    return 0;
}