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\n",tmp);
}
return 0;
}
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