ACM_高次同余方程

/*poj 3243 
 *解决高次同余方程的应用，已知 X^Y = K mod Z, 及X,Z,K的值，求 Y 的值 
*/

#include<cstdio>  
#include<cstring>  
#include<cmath>  
using namespace std;  
#define lint __int64  
#define MAXN 131071  
struct HashNode { lint data, id, next; };  
HashNode hash[MAXN<<1];  
bool flag[MAXN<<1];  
lint top;  
  
void Insert ( lint a, lint b )  
{  
    lint k = b & MAXN;  
    if ( flag[k] == false )  
    {  
        flag[k] = true;  
        hash[k].next = -1;  
        hash[k].id = a;  
        hash[k].data = b;  
        return;  
    }  
    while( hash[k].next != -1 )  
    {  
        if( hash[k].data == b ) return;  
        k = hash[k].next;  
    }  
    if ( hash[k].data == b ) return;  
    hash[k].next = ++top;  
    hash[top].next = -1;  
    hash[top].id = a;  
    hash[top].data = b;  
}  
  
lint Find ( lint b )  
{  
    lint k = b & MAXN;  
    if( flag[k] == false ) return -1;  
    while ( k != -1 )  
    {  
        if( hash[k].data == b ) return hash[k].id;  
        k = hash[k].next;  
    }  
    return -1;  
}  
  
lint gcd ( lint a, lint b )  
{  
    return b ? gcd ( b, a % b ) : a;  
}  
  
lint ext_gcd (lint a, lint b, lint& x, lint& y )  
{  
    lint t, ret;  
    if ( b == 0 )  
    {  
        x = 1, y = 0;  
        return a;  
    }  
    ret = ext_gcd ( b, a % b, x, y );  
    t = x, x = y, y = t - a / b * y;  
    return ret;  
}  
  
lint mod_exp ( lint a, lint b, lint n )  
{  
    lint ret = 1;  
    a = a % n;  
    while ( b >= 1 )  
    {  
        if( b & 1 )  
            ret = ret * a % n;  
        a = a * a % n;  
        b >>= 1;  
    }  
    return ret;  
}  
  
lint BabyStep_GiantStep ( lint A, lint B, lint C )  
{  
    top = MAXN;  B %= C;  
    lint tmp = 1, i;  
    for ( i = 0; i <= 100; tmp = tmp * A % C, i++ )  
        if ( tmp == B % C ) return i;  
  
    lint D = 1, cnt = 0;  
    while( (tmp = gcd(A,C)) !=1 )  
    {  
        if( B % tmp ) return -1;  
        C /= tmp;  
        B /= tmp;  
        D = D * A / tmp % C;  
        cnt++;  
    }  
  
    lint M = (lint)ceil(sqrt(C+0.0));  
    for ( tmp = 1, i = 0; i <= M; tmp = tmp * A % C, i++ )  
        Insert ( i, tmp );  
  
    lint x, y, K = mod_exp( A, M, C );  
    for ( i = 0; i <= M; i++ )  
    {  
        ext_gcd ( D, C, x, y ); // D * X = 1 ( mod C )  
        tmp = ((B * x) % C + C) % C;  
        if( (y = Find(tmp)) != -1 )  
            return i * M + y + cnt;  
        D = D * K % C;  
    }  
    return -1;  
}  
  
int main()  
{  
    lint A, B, C;  
    while( scanf("%I64d%I64d%I64d",&A,&C,&B ) !=EOF )  
    {  
        if ( !A && !B && !C ) break;  
        memset(flag,0,sizeof(flag));  
        lint tmp = BabyStep_GiantStep ( A, B, C );  
        if ( tmp == -1 )puts("No Solution");  
        else printf("%I64d
",tmp);  
    }  
    return 0;  
}