给定项数、公比、模数,求首项为1的等比数列的和
#include<iostream> #include<cstdio> #include<string> #include<cstring> #include<algorithm> #include<vector> #include<cmath> #define ll long long using namespace std; ll n,k,p; ll sum,numa,numb; ll euler_phi(ll x){ ll m = (int)sqrt(x+0.5); ll ans = x; for(int i = 2;i <= m;i++){ if(x % i == 0){ ans = ans / i * (i-1); while(x % i == 0) x /= i; } } if(x > 1) ans = ans / x * (x-1); return ans; } ll q_mul(ll a,ll b,ll mod){ ll ans = 0; while(b){ if(b&1){ b--; ans = (ans + a) % mod; } b/=2; a = (a + a) % mod; } return ans; } ll q_pow(ll a,ll b,ll mod){ ll ans = 1; while(b){ if(b&1){ ans = q_mul(ans,a,mod); } b/=2; a = q_mul(a,a,mod); } return ans; } ll inv(ll a,ll n){ return q_pow(a,euler_phi(n)-1,n); } int main(){ //freopen("sunshine.in","r",stdin); //freopen("sunshine.out","w",stdout); cin>>n>>k>>p; numa = (q_pow(k,n,p) + p - 1) % p; numb = inv(k-1,p); sum = q_mul(numa,numb,p); cout<<sum; return 0; }
时间: 2024-10-12 23:42:25