Submission #1257879

#	Time	Username	Problem	Language	Result	Execution time	Memory
1257879		ntabc05101	Potemkin cycle (CEOI15_indcyc)	C++20	50 / 100	150 ms	2236 KiB

indcyc

#include <bits/stdc++.h>
using namespace std;

#define MASK(i) (1LL << (i))
#define BIT(x, i) (((x) >> (i)) & 1LL)

using ll = long long;

const int mxn = 9 + 1e6;
const int inf = 0x3f3f3f3f;
const ll lnf = 0x3f3f3f3f3f3f3f3f;

int n, m;
vector<vector<int>> adj;
vector<array<int, 2>> e;

namespace SUB1 {
  bool check() {
    return (n <= 10 && m <= 45);
  }

  vector<int> par;
  vector<bool> used; 

  void dfs(int u, int cnt) {
    if (cnt >= 4) {
      vector<int> res;
      while (u) {
        res.push_back(u);
        u = par[u];
      }
      reverse(begin(res), end(res));
      if (binary_search(begin(adj[res.back()]), end(adj[res.back()]), res.front())) {
        for (auto &x : res) {
          cout << x << " ";
        }
        exit(0);
      }
    }
    used[u] = true;
    for (auto &v : adj[u]) {
      if (!used[v]) {
        par[v] = u;
        dfs(v, cnt + 1);
      }
    }
    used[u] = false;
  }

  void solve() {
    used.resize(n + 1);
    par.resize(n + 1);
    for (int i = 1; i <= n; ++i) {
      sort(begin(adj[i]), end(adj[i]));
    }
    for (int i = 1; i <= n; ++i) {
      dfs(i, 0);
    }
    cout << "no\n";
  }
}

namespace SUBFULL {
  void solve() {
    vector<int> dist(n + 1), par(n + 1);
    deque<int> q;
    e.resize(unique(begin(e), end(e)) - begin(e));
    for (auto &x : e) {
      fill(begin(dist), end(dist), -1);
      fill(begin(par), end(par), -1);
      while (!q.empty()) {
        q.pop_back();
      }
      dist[x[0]] = 0;
      q.push_back(x[0]);
      bool f = false;
      while (!q.empty()) {
        int u = q.front();
        q.pop_front();
        for (auto &v : adj[u]) {
          if ((u == x[0] && v == x[1]) || (u == x[1] && v == x[0])) {
            continue;
          }
          if (!~dist[v]) {
            dist[v] = dist[u] + 1;
            par[v] = u;
            if (v == x[1]) {
              f = true;
              break;
            }
            q.push_back(v);
          }
        }
        if (f) {
          break;
        }
      }
      if (f) {
        int len = dist[x[1]];
        if (len >= 3) {
          int s = x[1];
          vector<int> res;
          while (~s) {
            res.push_back(s);
            s = par[s];
          }
          reverse(begin(res), end(res));
          for (auto &x : res) {
            cout << x << " ";
          }
          return;
        }
      }
    }
    cout << "no\n";
  }
}

void _27augain(void) {
  cin >> n >> m;
  adj.resize(n + 1);
  for (int i = 0; i < m; ++i) {
    int u, v;
    cin >> u >> v;
    adj[u].push_back(v);
    adj[v].push_back(u);
    e.push_back({u, v});
  }
  SUBFULL::solve();
}

int32_t main(void) {
#define task "27augain"
  cin.tie(0)->sync_with_stdio(0);
  for (string iext : {"in", "inp"}) {
    if (fopen((task "." + iext).c_str(), "r")) {
      freopen((task "." + iext).c_str(), "r", stdin);
      freopen(task ".out", "w", stdout);
    }
  }
  int testcase = 1;
  // cin >> testcase;
  while (testcase--) {
    _27augain();
  }
  return 0;
}

Compilation message (stderr)

indcyc.cpp: In function 'int32_t main()':
indcyc.cpp:137:14: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  137 |       freopen((task "." + iext).c_str(), "r", stdin);
      |       ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
indcyc.cpp:138:14: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  138 |       freopen(task ".out", "w", stdout);
      |       ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 10 / 10
• Subtask 2: 10 / 10
• Subtask 3: 0 / 10
• Subtask 4: 10 / 10
• Subtask 5: 0 / 10
• Subtask 6: 10 / 10
• Subtask 7: 0 / 10
• Subtask 8: 10 / 10
• Subtask 9: 0 / 10
• Subtask 10: 0 / 10