제출 #539094

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
539094		alextodoran	Pipes (CEOI15_pipes)	C++17	0 / 100	1101 ms	13584 KiB

pipes

/**
 ____ ____ ____ ____ ____
||a |||t |||o |||d |||o ||
||__|||__|||__|||__|||__||
|/__\|/__\|/__\|/__\|/__\|

**/

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int N_MAX = (int) 1e5;

int N, M;

struct DSU {
    int root[N_MAX + 2];
    void init () {
        iota(root + 1, root + N + 1, 1);
    }
    int findRoot (int u) {
        return (root[u] == u ? u : root[u] = findRoot(root[u]));
    }
    bool join (int u, int v) {
        u = findRoot(u);
        v = findRoot(v);
        root[u] = v;
        return u != v;
    }
};
DSU A, B;

vector <int> adj[N_MAX + 2];

void addEdge (int u, int v) {
    adj[u].push_back(v);
    adj[v].push_back(u);
}

vector <pair <int, int>> bridges;
int level[N_MAX + 2];

int dfs (int u, int parent = -1) {
    int minLevel = level[u];
    bool par = false;
    for (int v : adj[u]) {
        if (level[v] == -1) {
            level[v] = level[u] + 1;
            minLevel = min(minLevel, dfs(v, u));
        } else if (v == parent && par == false) {
            par = true;
        } else {
            minLevel = min(minLevel, level[v]);
        }
    }
    if (parent != -1 && minLevel == level[u]) {
        bridges.push_back(make_pair(parent, u));
    }
    return minLevel;
}
void dfs () {
    fill(level + 1, level + N + 1, -1);
    for (int u = 1; u <= N; u++) {
        if (level[u] == -1) {
            dfs(u);
        }
    }
}

int main () {
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    cin >> N >> M;
    A.init(); B.init();
    int cnt = 0;
    while (M--) {
        int u, v;
        cin >> u >> v;
        if (A.join(u, v) == true) {
            addEdge(u, v); cnt++;
        } else if (B.join(u, v) == true) {
            addEdge(u, v); cnt++;
        }
    }
    assert(cnt <= (N - 1) * 2);

    dfs();
    for (pair <int, int> e : bridges) {
        cout << e.first << " " << e.second << "\n";
    }

    return 0;
}

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