扩展BSGS学习笔记

最新推荐文章于 2024-08-11 09:00:00 发布

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最新推荐文章于 2024-08-11 09:00:00 发布

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原文链接：http://www.cnblogs.com/ChiTongZ/p/11261896.html

Attention

在哈希表中查询的时候答案不能取模，可以证明是错的。

#include <bits/stdc++.h>
#define ll long long
#define xx first
#define yy second
using namespace std;
int a, p, b;
inline int gcd (int m, int n) {return (!n) ? m : gcd (n, m % n);}
unordered_map<int, int> mp;
inline int Pow (int u, int v, int mod) {
    int tot = 1, base = u % mod;
    while (v) {
        if (v & 1) {tot = 1LL * tot * base % mod;}
        base = 1LL * base * base % mod; v /= 2;
    }
    return tot;
}
inline void solve () {
    if (b == 1) {printf ("0\n"); return ;}
    int d = gcd (a, p), k = 1, cnt = 0;
    while (d > 1) {
        if (b % d) {printf ("No Solution\n"); return ;}
        cnt++, k = 1LL * k * (a / d) % p;
        p /= d, b /= d;
        if (b == k) {printf ("%d\n", cnt); return ;}
        d = gcd (a, p);
    }
    mp.clear ();
    int sz = sqrt (p) + 1, step = Pow (a, sz, p);
    for (int i = 1; i <= sz; ++i) {
        k = 1LL * k * step % p;
        if (!mp.count (k) || mp[k] > i * sz) {mp[k] = i * sz;}
    }
    int cdt = 1;
    bool flag = false; int ans = INT_MAX;
    for (int i = 0; i <= sz; ++i) {
        if (i) {cdt = 1LL * cdt * a % p;}
        if (mp[1LL * cdt * b % p]) {
            int tans = mp[1LL * cdt * b % p] - i + cnt;
//          tans = (tans % p + p) % p;
            ans = min (ans, tans);
            flag = true;
        }
    }
    if (flag) {printf ("%d\n", ans);return ;}
    printf ("No Solution\n");
}
int main () {
    while (scanf ("%d%d%d", &a, &p, &b) == 3) {
        if (a == 0 && b == 0 && p == 0) {return 0;}
        a %= p;
        b %= p;
        solve ();
    }
    return 0;
}

这是洛谷的模板题，注释掉的地方不能要。

转载于:https://www.cnblogs.com/ChiTongZ/p/11261896.html