【洛谷P2485】计算器

BSGS模板题

代码如下

#include <bits/stdc++.h>

using namespace std;

typedef long long LL;

LL fpow(LL a, LL b, LL c) {
  LL ret = 1 % c;
  for (; b; b >>= 1, a = a * a % c) {
    if (b & 1) {
      ret = ret * a % c;
    }
  }
  return ret;
}
LL bsgs(LL a, LL b, LL p) {
  b %= p;
  unordered_map<LL, LL> mp;
  LL t = (LL)sqrt(p) + 1;
  for (int i = 0; i < t; i++) {
    LL val = b * fpow(a, i, p) % p;
    mp[val] = i;
  }
  a = fpow(a, t, p);
  if (a == 0) return b == 0 ? 1 : -1;
  if (b == 0) return -1;
  if (b == 1) return 0;
  for (int i = 0; i <= t; i++) {
    LL val = fpow(a, i, p);
    LL j = mp.find(val) == mp.end() ? -1 : mp[val];
    if (j >= 0 && i * t - j >= 0) {
      return i * t - j;
    }
  }
  return -1;
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
  int T, opt;
  cin >> T >> opt;
  while (T--) {
    LL y, z, p;
    cin >> y >> z >> p;
    if (opt == 1) {
      cout << fpow(y, z, p) << endl;
    } else if (opt == 2) {
      if (y % p == 0) {
        cout << "Orz, I cannot find x!" << endl;
      } else {
        cout << z * fpow(y, p - 2, p) % p << endl;
      }
    } else {
      LL ret = bsgs(y, z, p);
      if (ret == -1) {
        cout << "Orz, I cannot find x!" << endl;
      } else {
        cout << ret << endl;
      }
    }
  }
  return 0;
}