exBSGS

模板

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
const int HashMod = 191981;
long long a, b, p;
struct HashTable {
	struct Line {int u, v, next;} e[100000];
	int h[HashMod], cnt;
	void add(int u, int v, int w) {e[++ cnt] = (Line){w, v, h[u]}; h[u] = cnt;}
	void clear() {memset(h, 0, sizeof(h)); cnt = 0;}
	void insert(int x, int i) {
		int k = x % HashMod;
		add(k, i, x);
	}
	int query(int x) {
		for(int i = h[x % HashMod]; i; i = e[i].next)
			if(e[i].u == x) return e[i].v;
		return -1;
	}
} hs;
long long gcd (long long a, long long b) {
	return !b ? a : gcd(b, a % b);
}
long long exgcd (long long a, long long b, long long &x, long long &y) {
    if (!b) {
        x = 1;
        y = 0;
        return a;
    }
    long long d = exgcd(b, a % b, x, y), z;
    z = x;
    x = y;
    y = z - a / b * y;
    return d;
}
long long inv (long long a, long long b) {
	long long x, y;
	exgcd(a, b, x, y);
	return (x % b + b) % b;
}
long long BSGS (long long a, long long b, long long p) {
	long long s = sqrt(p) + 1, r = 1, sr = 1;
	hs.clear();
	for (int i = 0; i < s; i ++) {
		hs.insert(r * b % p, i);
		r = r * a % p;
	}
	sr = r;
	for (int i = 1; i <= s; i ++) {
        int q = hs.query(sr);
		if (q != -1) return s * i - q;
		sr = sr * r % p;
	}
	return -1;
}
long long exBSGS (long long x, long long y, long long p) {
	if (y == 1 || p == 1) return 0;
	long long g = gcd(x, p), k = 0, nx = 1, res;
	while (g > 1) {
		if (y % g) return -1;
		k ++;
		y /= g;
		p /= g;
		nx = nx * (x / g) % p;
		if (nx == y) return k;
		g = gcd(x, p);
	}
	res = BSGS(x, y * inv(nx, p) % p, p);
	if (res == -1) return -1;
	else return res + k;
}
int main () {
	scanf("%lld%lld%lld", &a, &p, &b);
	while (a || p || b) {
		a %= p;
		b %= p;
		long long res = exBSGS(a, b, p);
		if (res == -1) printf("No Solution\n");
		else printf("%lld\n", res);
		scanf("%lld%lld%lld", &a, &p, &b);
	}
    return 0;
}