P2303 [SDOI2012] Longge 的问题

P2303 [SDOI2012] Longge 的问题

直接上莫反即可。

查看代码

#include <cstdio>
using namespace std;
template <class Type>
void read(Type &x)
{
    char c;
    bool flag = false;
    while ((c = getchar()) < '0' || c > '9')
        c == '-' && (flag = true);
    x = c - '0';
    while ((c = getchar()) >= '0' && c <= '9')
        x = (x << 3) + (x << 1) + c - '0';
    flag && (x = ~x + 1);
}
template <class Type>
void write(Type x)
{
    x < 0 && (putchar('-'), x = ~x + 1);
    x > 9 && (write(x / 10), 0);
    putchar(x % 10 + '0');
}
typedef long long LL;
LL n;
LL phi (LL x)
{
    LL res = x;
    for (LL i = 2; i * i <= x; i++)
        if (x % i == 0)
        {
            res = res / i * (i - 1);
            while (x % i == 0)
                x /= i;
        }
    x > 1 && (res /= x, res *= (x - 1));
    return res;
}
int main ()
{
    read(n);
    LL res = 0;
    for (LL i = 1; i * i <= n; i++)
        if (n % i == 0)
        {
            res += i * phi(n / i);
            i * i ^ n && (res += n / i * phi(i));
        }
    write(res);
    return 0;
}