Submission #1259609

#	Time	Username	Problem	Language	Result	Execution time	Memory
1259609		nqknht	Potemkin cycle (CEOI15_indcyc)	C++20	100 / 100	207 ms	91768 KiB

indcyc

#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define dl double
#define st first
#define nd second
#define II pair <int, int>

using namespace std;

const int N = 1 + 1e3;
const int inf = 7 + 1e9;

struct Edge {
    int u, v;
};

int s = -1, t = -1;
vector <Edge> e;
vector <int> deg, vis, p;
vector <vector <int>> adj;

void dfs(int u) {
    if (s >= 0)
        return;
    vis[u] = 1;
    for (int v : adj[u]) {
        if (!vis[v]) {
            p[v] = u;
            // cout << "- " << u << ' ' << v << '\n';
            dfs(v);
        }
        else if (vis[v] == 1) {
            s = u;
            t = v;
        }
        if (s >= 0)
            return;
    }
    vis[u] = 2;
}

int main() {
#define TASKNAME ""
    ios_base :: sync_with_stdio (0);
    cin.tie (0);
    if ( fopen( TASKNAME".inp", "r" ) ) {
        freopen (TASKNAME".inp", "r", stdin);
        freopen (TASKNAME".out", "w", stdout);
    }
    int n, m; 
    cin >> n >> m;
    e.resize(2 * m + 2);
    vector <vector <int>> f(n + 1, vector <int> (n + 1, 0));
    for (int i = 1; i <= m; i ++) {
        cin >> e[i].u >> e[i].v;
        f[e[i].u][e[i].v] = i * 2;
        f[e[i].v][e[i].u] = i * 2 + 1;
    }
    adj.resize(2 * m + 2);
    for (int i = 1; i <= m; i ++) {
        int u = e[i].u, v = e[i].v;
        for (int w = 1; w <= n; w ++)
            if (w != u && w != v) {
                if (f[v][w] && !f[u][w])
                    adj[i * 2].push_back(f[v][w]);
                if (f[u][w] && !f[v][w])
                    adj[i * 2 + 1].push_back(f[u][w]);
            }
    }
    for (int i = m; i > 0; i --) {
        e[i * 2] = e[i];
        e[i * 2 + 1] = {e[i].v, e[i].u};
    }
    vis.assign(2 * m + 2, 0);
    p.assign(2 * m + 2, 0);
    for (int i = 2; i < m * 2 + 2; i ++)
        if (!vis[i]) {
            p[i] = 0;
            dfs(i);
            if (s >= 0)
                break;
        }
    if (s < 0) {
        cout << "no";
        return 0;
    }
    vector <int> c;
    c.push_back(e[s].u);
    while (s != t) {
        s = p[s];
        c.push_back(e[s].u);
    }
    for (int i = (int)c.size() - 1; i >= 0; i --)
        for (int j = i + 3; j < c.size(); j ++)
            if (f[c[i]][c[j]]) {
                for (int u = i; u <= j; u ++)
                    cout << c[u] << ' ';
                return 0;
            }
    return 0;
}

Compilation message (stderr)

indcyc.cpp: In function 'int main()':
indcyc.cpp:48:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   48 |         freopen (TASKNAME".inp", "r", stdin);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
indcyc.cpp:49:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   49 |         freopen (TASKNAME".out", "w", stdout);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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