HDU 6051原根 + 欧拉函数

题解:

主要是原根的幂表示[1, p - 1],
然后转换
hint里的公式:
找了一篇证明:http://blog.csdn.net/Clove_unique/article/details/53152473

代码:

#include <cstdio>#include <cstring>#include <algorithm>using namespace std;typedef long long ll;const ll mod = 1e9 + 7;ll m, p;ll getPhi(ll x){    ll ret = x;    for(ll i = 2; i * i <= x; ++i)    {        if(x % i == 0)        {            while(x % i == 0) x /= i;            ret -= ret / i;        }    }    if(x > 1) ret -= ret / x;    return ret;}ll get(int n, int fac){    return (ll)fac * fac % mod * (((ll)n * getPhi(n) + (n == 1)) / 2) % mod;}int cal(int x){    int ret = 0;    for(int i = 1; (ll)i * i <= x; ++i)    {        if(x % i == 0)        {            ret = (ret + get(x / i, i)) % mod;            if(i != x / i) ret = (ret + get(i, x / i)) % mod;        }    }    ret -= ((ll)x * (x + 1) / 2) % mod;    ret = (ret % mod + mod) % mod;    return ret;}int main(){    int t;    scanf("%d", &t);    int kas = 0;    while(t--)    {        scanf("%lld%lld", &m, &p);        ll res = cal(p - 1);        printf("Case #%d: %d\n", ++kas, (res * m) % mod);    }    return 0;}