Submission #1176303

#	Time	Username	Problem	Language	Result	Execution time	Memory
1176303		anha3k25cvp	Potemkin cycle (CEOI15_indcyc)	C++20	0 / 100	17 ms	5960 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 node = 0;
vector <Edge> e;
vector <int> l, r, p, used;
vector <vector <int>> adj;

void dfs(int u) {
    l[u] = ++ node;
    for (int i : adj[u]) {
        int v = e[i].u + e[i].v - u;
        if (!l[v]) {
            p[v] = u;
            used[i] = 1;
            dfs(v);
        }
    }
    r[u] = node;
}

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(m + 1);
    adj.resize(n + 1);
    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;
        adj[e[i].u].push_back(i);
        adj[e[i].v].push_back(i);
    }
    l.assign(n + 1, 0);
    r.assign(n + 1, 0);
    p.assign(n + 1, 0);
    used.assign(m + 1, 0);
    for (int i = 1; i <= n; i ++)
        if (!l[i])
            dfs(i);
    for (int i = 1; i <= m; i ++) {
        if (l[e[i].u] > l[e[i].v])
            swap(e[i].u, e[i].v);
        f[e[i].u][e[i].v] = used[i] ^ 1;
    }
    vector <II> c;
    for (int i = 1; i <= n; i ++)
        c.push_back({l[i], i});
    sort(c.begin(), c.end());
    for (int i = n - 1; i >= 0; i --)
        for (int j = i + 2; j < n; j ++) {
            int u = c[i].nd, v = c[j].nd, u1, v1 = p[v];
            if (l[v] < l[u] || r[u] < l[v])
                continue;
            for (int id : adj[u]) {
                int v2 = e[id].u + e[id].v - u;
                if (l[v2] <= l[v] && l[v] <= r[v2]) {
                    u1 = v2;
                    break;
                }
            }
            f[u][v] += f[u][v1] + f[u1][v] - f[u1][v1];
        }
    for (int i = 1; i <= m; i ++) {
        if (used[i])
            continue;
        int u = e[i].u, v = e[i].v;
        if (f[u][v] > 1)
            continue;
        vector <int> a = {v};
        while (v != u) {
            v = p[v];
            a.push_back(v);
        }
        if (a.size() > 3) {
            for (int u : a)
                cout << u << ' ';
            return 0;
        }
    }
    cout << "no";
    return 0;
}

Compilation message (stderr)

indcyc.cpp: In function 'int main()':
indcyc.cpp:41:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   41 |         freopen (TASKNAME".inp", "r", stdin);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~
indcyc.cpp:42:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   42 |         freopen (TASKNAME".out", "w", stdout);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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