BSGS

问题：

解法：

代码：

#include <iostream>  
#include <string.h>  
#include <stdio.h>  
#include <math.h>  
//#include <bits/stdc++.h>
using namespace std;
#define ll long long
ll x,y,hashmod=2277779;
ll top,hash[3000000],value[3000000],stack[3000000];
struct re
{
    ll locate(ll x)
    {
        ll h=x%hashmod;
        while (hash[h]!=-1 && hash[h]!=x) ++h;
        return(h);
    }
    void insert(ll x,ll y)
    {
        ll pos=locate(x);
        if (hash[pos]==-1)
        { 
        hash[pos]=x;value[pos]=y;stack[++top]=pos;
        } 
    }
    ll get(ll x)
    {
        ll pos=locate(x);
      if (hash[pos]==x) return(value[pos]);
      else return(-1);
    }
    void clear()
    {
        while (top>0) hash[stack[top--]]=-1;
  }
  void init()
  {
      memset(hash,0xFF,sizeof(hash));
  }
}hashh;
ll gcd(ll a,ll b,ll &x,ll &y)
{
    if (b==0)
    {
        x=1; y=0; return(a); 
  }
  ll tmp=gcd(b,a%b,y,x);
  y=y-(a/b)*x;
}
ll bsgs(ll a,ll b,ll c)
{
  ll sqrtn=(ll)ceil(sqrt(c));
  ll base=1;
  hashh.clear();
  for (ll i=0;i<sqrtn;i++)
  {
      hashh.insert(base,i);
      base=base*a %c;
  }
  ll d=1;
  for (ll i=0;i<sqrtn;i++)
  {
      gcd(d,c,x,y);
      x=(x*b%c+c)%c;
      ll j=hashh.get(x);
      if (j!=-1) return(i*sqrtn+j);
      d=d*base %c;
  }
  return -1;
}
int main()
{
    freopen("noip.in","r",stdin);
    freopen("noip.out","w",stdout);
    std::ios::sync_with_stdio(false);
    ll a,b,p;
    hashh.init();
    while (cin>>p>>a>>b)
    {
    ll ans=bsgs(a,b,p);
    if (ans==-1) cout<<"no solution"<<endl;
    else cout<<ans<<endl;
    }
    return(0);
}