EXBSGS模板

Posted 2021-02-01 lnxcj

 1 #include<cmath>
 2 #include<cstdio>
 3 #include<cstring>
 4 #include<algorithm>
 5 #define mod 600000
 6 using namespace std;
 7 int cnt,tot;
 8 int head[600005];
 9 long long a,b,c,x,y;
10 struct Edge{
11     int fr;
12     int val;
13     int nxt;
14     long long to;
15 }edge[600005];
16 void init(){
17     cnt=0;
18     memset(head,-1,sizeof(head));
19 }
20 void addedge(int u,long long v,int w){
21     edge[cnt].fr=u;
22     edge[cnt].to=v;
23     edge[cnt].val=w;
24     edge[cnt].nxt=head[u];
25     head[u]=cnt++;
26 }
27 long long exgcd(long long i,long long j,long long &x,long long &y){
28     if(!j){
29         x=1,y=0;
30         return i;
31     }
32     long long tmp=exgcd(j,i%j,y,x);
33     y-=(i/j)*x;
34     return tmp;
35 }
36 long long BSGS(long long A,long long B,long long C){
37     init();
38     int m=sqrt(C);
39     long long mul1=1;
40     long long mul2=1;
41     for(int i=1;i<=m;i++){
42         mul1=(mul1*A)%C;
43         long long ad=(mul1*B)%C;
44         if(!ad)return -1;
45         addedge(ad%mod,ad,i);
46     }
47     for(int i=1;i<=m+3;i++){
48         mul2=(mul2*mul1)%C;
49         for(int j=head[mul2%mod];j!=-1;j=edge[j].nxt){
50             long long v=edge[j].to;
51             if(v==mul2)return 1ll*i*m-1ll*edge[j].val;
52         }
53     }
54     return -1;
55 }
56 void EXBSGS(long long A,long long B,long long C){
57     tot=0;
58     long long d=exgcd(A,C,x,y);
59     long long mul=1;
60     while(d!=1){
61         if(B%d){
62             if(B==1){
63                 printf("0
");
64                 return;
65             }else{
66                 printf("No Solution
");
67                 return;
68             }
69         }
70         B/=d,C/=d,tot++,mul*=(A/d);
71         d=exgcd(A,C,x,y);
72     }
73     d=exgcd(mul,C,x,y);
74     x=(x%C+C)%C;
75     long long ans=BSGS(A,(B*x)%C,C);
76     if(ans!=-1)printf("%lld
",ans+tot);
77     else printf("No Solution
");
78 }
79 int main(){
80     while(1){
81         scanf("%lld%lld%lld",&a,&b,&c);
82         if(!a&&!b&&!c)break;
83         EXBSGS(a,c,b);
84     }
85     return 0;
86 }