Submission #1285401

#	Time	Username	Problem	Language	Result	Execution time	Memory
1285401		lmquan	Three Friends (BOI14_friends)	C++20	0 / 100	1 ms	568 KiB

friends

#define taskname ""
#include <bits/stdc++.h>
using namespace std;
const int kBase = 647;
const int kMod = 454539497;

int main() {
  if (fopen(taskname".inp", "r")) {
    freopen(taskname".inp", "r", stdin);
    freopen(taskname".out", "w", stdout);
  }
  ios_base::sync_with_stdio(false);
  cin.tie(nullptr);

  int n;
  string u;
  cin >> u;
  n = (int)u.size();

  if (n % 2 == 0) {
    cout << "NOT POSSIBLE";
  } else {
    vector<int> p(n), q(n);
    for (int i = 0; i < n; i++) {
      p[i] = ((i > 0 ? 1LL * p[i - 1] * kBase : 0) + (u[i] - 'A' + 1)) % kMod;
      q[i] = (i > 0 ? 1LL * q[i - 1] * kBase : 1) % kMod;
    }
    auto G = [&](int l, int r) -> int {
      return ((p[r] - 1LL * p[l - 1] * q[r - l + 1]) % kMod + kMod) % kMod;
    };
    string k = "";
    int v;
    for (int i = 0; i < n; i++) {
      int j = (i > 0 ? p[min(n / 2 - 1, i - 1)] : 0);
      int x = (1LL * j * q[max(0, n / 2 - i)] + (i < n / 2 ? G(i + 1, n / 2) : 0)) % kMod;
      int y = (i <= n / 2 ? G(n / 2 + 1, n - 1) : 1LL * G(n / 2, i - 1) * q[n - i - 1] + G(i + 1, n - 1)) % kMod;
      if (x == y) {
        if (!k.empty() && x != v) {
          cout << "NOT UNIQUE";
          return 0;
        }
        if (k.empty()) {
          if (i <= n / 2) {
            k = u.substr(n / 2 + 1, n / 2);
          } else {
            k = u.substr(0, n / 2);
          }
        }
        v = x;
      }
    }
    cout << (k.empty() ? "NOT POSSIBLE" : k);
  }
  return 0;
}

Compilation message (stderr)

friends.cpp: In function 'int main()':
friends.cpp:9:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
    9 |     freopen(taskname".inp", "r", stdin);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
friends.cpp:10:12: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   10 |     freopen(taskname".out", "w", stdout);
      |     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 35
• Subtask 2: 0 / 65