逆元
题目连接:https://scut.online/problem.php?id=97
算出y在p下的逆元,枚举z就可以求出x了
1 #include<cstdio> 2 #include<cstring> 3 #include<algorithm> 4 using namespace std; 5 #define ll long long 6 7 ll qpow(ll a,ll b, ll m) 8 { 9 ll ans=1,temp=a%m; 10 while(b) 11 { 12 if(b&1) ans=(ans*temp)%m; 13 b>>=1; 14 temp=(temp*temp)%m; 15 } 16 return ans; 17 } 18 19 int main() 20 { 21 int y,p,k; 22 23 int t; 24 scanf("%d",&t); 25 while(t--) 26 { 27 scanf("%d%d%d",&y,&k,&p); 28 ll ans=0; 29 if(y!=0) 30 { 31 ll inv=qpow(y,p-2,p); //求逆元 32 int n=min(1000000,p-1); 33 k=min(k,n); 34 for(int i=0;i<=k;i++) 35 ans=ans+(i*inv%p); 36 } 37 else 38 ans=(p-1)*p/2; 39 printf("%lld\n",ans); 40 } 41 }