Submission #393141

#	Time	Username	Problem	Language	Result	Execution time	Memory
393141		dolphingarlic	Potemkin cycle (CEOI15_indcyc)	C++14	0 / 100	454 ms	96600 KiB

indcyc

/*
CEOI 2016 Potemkin Cycle
- Let each edge (u, v) represent a node (uv) in graph H
- There is an edge between (uv) and (vw) in H iff (uw) doesn't exist
    - This means that there are no cycles of length 3 in H
    - We can construct H in O(NR) time
- An answer exists iff a cycle exists in H; run DFS to find a cycle
*/

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

int u[200001], v[200001], adj[1001][1001];
vector<int> graph[100001];
int prv[100001];

void dfs(int node, int parent = -1) {
    prv[node] = parent;
    for (int i : graph[node]) if (i != parent) {
        if (prv[i]) {
            vector<int> edges;
            int curr = node;
            while (curr != prv[i]) {
                edges.push_back(curr);
                curr = prv[curr];
            }
            int m = edges.size();
            for (int j = 0; j < m; j++) cout << u[j];
            exit(0);
        } else dfs(i, node);
    }
}

int main() {
    cin.tie(0)->sync_with_stdio(0);
    int n, r;
    cin >> n >> r;
    for (int i = 1; i <= r; i++) {
        cin >> u[i] >> v[i];
        u[i + r] = v[i], v[i + r] = u[i];
        adj[u[i]][v[i]] = i, adj[v[i]][u[i]] = i + r;
    }

    for (int i = 1; i <= 2 * r; i++) {
        for (int j = 1; j <= n; j++) if (j != u[i]) {
            if (adj[v[i]][j] && !adj[u[i]][j]) {
                graph[i].push_back(adj[v[i]][j]);
                graph[adj[v[i]][j]].push_back(i);
            }
        }
    }

    for (int i = 1; i <= 2 * r; i++) if (!prv[i]) dfs(i);
    cout << "no";
    return 0;
}

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