Submission #1257995

#TimeUsernameProblemLanguageResultExecution timeMemory
1257995duyanhloveavPotemkin cycle (CEOI15_indcyc)C++20
100 / 100
72 ms9288 KiB
#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; namespace SUB1 { bool check() { return (n <= 10 && m <= 45); } vector<int> par; vector<char> used; void dfs(int u, int s, int h) { if (h >= 4) { vector<int> res; int cur = u; while (cur) { res.push_back(cur); cur = par[cur]; } reverse(begin(res), end(res)); if (binary_search(begin(adj[res.back()]), end(adj[res.back()]), res.front())) { bool f = false; for (int i = 0; i < (int)res.size() && !f; ++i) { for (int j = i + 1; j < (int)res.size(); ++j) { if (j == i + 1 || (i == 0 && j == (int)res.size() - 1)) continue; if (binary_search(begin(adj[res[i]]), end(adj[res[i]]), res[j])) { f = true; break; } } } if (!f) { for (auto &v : res) { cout << v << " "; } cout << "\n"; exit(0); } } } used[u] = true; for (auto &v : adj[u]) { if (!used[v]) { par[v] = u; dfs(v, s, h + 1); } } used[u] = false; } void solve() { par.assign(n + 1, 0); used.assign(n + 1, 0); for (int i = 1; i <= n; ++i) { sort(begin(adj[i]), end(adj[i])); } for (int i = 1; i <= n; ++i) { par[i] = 0; dfs(i, i, 1); } cout << "no\n"; } } namespace SUBFULL { /* Ta gọi danh sách chu trình là : c[1], c[2], ..., c[n], c[1] * Nếu tồn tại cặp (c[i], c[i + 2]) -> sẽ không thỏa mãn * Ngược lại, nếu tồn tại cặp (c[i], c[i + 3]) -> Dãy c[i], c[i + 1], c[i + 2], c[i + 3] lại là chu trình thỏa mãn đề bài * Dễ dàng chứng minh với các trường hợp còn lại (c[i], c[i + 4]), ... => Ta thấy chỉ cần kiểm soát xem có cặp (c[i], c[i + 2]) hay không */ void solve() { vector<vector<bool>> check(n + 1, vector<bool>(n + 1)); for (int i = 1; i <= n; ++i) { check[i][i] = true; for (auto &j : adj[i]) { check[i][j] = true; } } vector<vector<int>> used(n + 1, vector<int>(n + 1)), par(n + 1, vector<int>(n + 1)); auto dfs = [&] (auto &&self, int u, int v, int p) -> void { used[u][v] = 1; par[u][v] = p; for (auto &x : adj[v]) { if (check[u][x]) { continue; } if (used[v][x] == 1) { while (v ^ x) { cout << v << " "; int mid = u; u = par[u][v]; v = mid; } cout << x; exit(0); } else if (!used[v][x]) { self(self, v, x, u); } } used[u][v] = 2; }; for (int i = 1; i + 1 <= n; ++i) { for (int j = i + 1; j <= n; ++j) { if (check[i][j] && !used[i][j]) { dfs(dfs, i, j, 0); } } } 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); } if (SUB1::check()) { SUB1::solve(); return; } 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:150:14: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  150 |       freopen((task "." + iext).c_str(), "r", stdin);
      |       ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
indcyc.cpp:151:14: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
  151 |       freopen(task ".out", "w", stdout);
      |       ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
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