Submission #958667

#	Time	Username	Problem	Language	Result	Execution time	Memory
958667		Ghetto	Potemkin cycle (CEOI15_indcyc)	C++17	20 / 100	36 ms	3156 KiB

indcyc

#include <bits/stdc++.h>
using namespace std;
using pii = pair<int, int>;
const int MAX_N = 1e3 + 5;

int n, r;
vector<int> adj[MAX_N];

int depth[MAX_N];
int par[MAX_N];
unordered_set<int> children[MAX_N];
vector<pii> back_adj[MAX_N]; // {depth, node}

bool seen[MAX_N];
void dfs1(int u, int d) {
    seen[u] = true;
    depth[u] = d;
    for (int v : adj[u]) {
        if (seen[v]) continue;
        par[v] = u;
        children[u].insert(v);
        dfs1(v, d + 1);
    }
}

void precomp() {
    for (int i = 1; i <= n; i++) {
        if (seen[i]) continue;
        dfs1(i, 0);
    }

    for (int i = 1; i <= n; i++) {
        for (int j : adj[i]) {
            if (depth[j] > depth[i] - 2) continue; // No double edge between child and par
            back_adj[i].push_back({depth[j], j});
        }

        sort(back_adj[i].rbegin(), back_adj[i].rend());
    }
}

void dfs2(int u, int max_depth) {
    for (pii el : back_adj[u]) {
        int v = el.second;
        assert(depth[v] < depth[u]);
        if (depth[u] - depth[v] < 3 || max_depth >= depth[v])
            max_depth = max(max_depth, depth[v]);
        else {
            int w = u;
            while (true) {
                cout << w << " ";
                if (w == v) break;
                w = par[w];
            }
            exit(0);
        }
    }

    for (int v : children[u]) dfs2(v, max_depth);
}

int main() {
    // freopen("cycle.in", "r", stdin);

    cin >> n >> r;
    for (int i = 1; i <= r; i++) {
        int u, v; cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
    }

    precomp();

    // for (int i = 1; i <= n; i++) {
    //     cout << i << ": ";
    //     for (int j : children[i]) cout << j << " ";
    //     cout << endl;
    // }
    
    for (int i = 1; i <= n; i++) {
        if (par[i]) continue;
        dfs2(i, -1);
    }
    cout << "no" << '\n';
}

• Subtask 1: 10 / 10
• Subtask 2: 0 / 10
• Subtask 3: 0 / 10
• Subtask 4: 10 / 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