裸题(n是素数)
#include <stdio.h>
#include <string.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <time.h>
using namespace std;
//baby_step giant_step
// a^x = b (mod n) n为素数,a,b < n
// 求解上式 0<=x < n的解
#define MOD 76543
int hs[MOD],head[MOD],Next[MOD],id[MOD],top;
void insert(int x,int y)
{
int k = x%MOD;
hs[top] = x, id[top] = y, Next[top] = head[k], head[k] = top++;
}
int find(int x)
{
int k = x%MOD;
for(int i = head[k]; i != -1; i = Next[i])
if(hs[i] == x)
return id[i];
return -1;
}
int BSGS(int a,int b,int n)
{
memset(head,-1,sizeof(head));
top = 1;
if(b == 1)return 0;
int m = sqrt(n*1.0), j;
long long x = 1, p = 1;
for(int i = 0; i < m; ++i, p = p*a%n)insert(p*b%n,i);
for(long long i = m; ;i += m)
{
if( (j = find(x = x*p%n)) != -1 )return i-j;
if(i > n)break;
}
return -1;
}
int main()
{
//freopen("in.txt","r",stdin);
//freopen("out.txt","w",stdout);
int a,b,n;
while(scanf("%d%d%d",&n,&a,&b) == 3)
{
int ans = BSGS(a,b,n);
if(ans == -1)printf("no solution\n");
else printf("%d\n",ans);
}
return 0;
}
扩展(n不一定是素数)
#include <cstdio>
#include <stack>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <iostream>
#include <map>
#include <vector>
#include <queue>
#include <set>
#define eps 1e-8
typedef long long ll;
const double PI = acos(-1.0);
const int maxn = 1e6;
const int INF = 0x3f3f3f;
const ll linf = 0x3f3f3f3f3f3f3f3f;
const int mod = 1e9+7;
using namespace std;
/*
* baby_step giant _step
* a^x = b(mod n) n不要求是素数
* 求解上式0 ≤ x < n的解
*/
#define MOD maxn
ll hs[MOD];
int head[MOD];
ll _next[MOD];
ll id[MOD];
int top;
void insert(ll x, ll y)
{
ll k = x % MOD;
hs[top] = x;
id[top] = y;
_next[top] = head[k];
head[k] = top++;
return ;
}
ll find(ll x)
{
ll k = x % MOD;
for (int i = head[k]; i != -1; i = _next[i])
{
if (hs[i] == x)
{
return id[i];
}
}
return -1;
}
ll BSGS(ll a, ll b, ll n)
{
memset(head, -1, sizeof(head));
top = 1;
if (b == 1)
{
return 0;
}
ll m = sqrt(n * 1.0), j;
long long x = 1, p = 1;
for (int i = 0; i < m; i++, p = p * a % n)
{
insert(p * b % n, i);
}
for (long long i = m; ; i+=m)
{
if ((j = find(x = x * p % n)) != -1)
{
return i - j;
}
if (i > n)
{
break;
}
}
return -1;
}
int main()
{
ios::sync_with_stdio(false);
ll X,Z,K;
while(cin>>X>>Z>>K && X+Z+K>0)
{
ll ans = BSGS(X,K,Z);
if(ans == -1)
{
cout<<"No Solution"<<endl;
continue;
}
cout<<ans<<endl;
}
return 0;
}