Submission #873144

#	Time	Username	Problem	Language	Result	Execution time	Memory
873144		Ghulam_Junaid	Pipes (CEOI15_pipes)	C++17	20 / 100	784 ms	65536 KiB

pipes

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

const int N = 1e5 + 10;
int par[N], par1[N], par2[N], h[N], mnh[N], edges;
bool vis[N];
vector<pair<int, int>> bridges, g[N];

int root1(int v){
    return (par1[v] == -1 ? v : par1[v] = root1(par1[v]));
}

int root2(int v){
    return (par2[v] == -1 ? v : par2[v] = root2(par2[v]));
}

void merge1(int u, int v){
    // cout << "merge1 : " << u << " " << v << endl;
    
    int r1 = root1(v);
    int r2 = root1(u);

    par1[r1] = r2;

    edges++;
    g[v].push_back({u, edges});
    g[u].push_back({v, edges});
}

void merge2(int u, int v){
    int r1 = root2(u);
    int r2 = root2(v);

    if (r1 == r2)
        return;

    par2[r1] = r2;

    edges++;
    g[v].push_back({u, edges});
    g[u].push_back({v, edges});
}

void dfs(int v, pair<int, int> prev = {-1, -1}){
    // cout << v << endl;
    vis[v] = 1;
    if (prev.first == -1)
        h[v] = 0;
    mnh[v] = h[v];
    for (auto [u, id] : g[v]){
       // if (v == 59 and u == 3)
       //      cout << "-------HERE---------- " << id << endl;
        if (prev.first == u and prev.second == id)
            continue;

        // cout << v << " -- " << u << endl;        
        mnh[v] = min(mnh[v], h[u]);

        if (vis[u])
            continue;

        // cout << "safe" << endl;

        h[u] = h[v] + 1;
        par[u] = v;
        dfs(u, {v, id});
        mnh[v] = min(mnh[v], mnh[u]);

        // cout << u << " : " << mnh[u] << endl;
        if (mnh[u] >= h[u])
            bridges.push_back({v, u});
    }
}
// 1 -- 2 -- 3 -- 59
// void print(int v){
//     cout << v << " : " << mnh[v] << endl;
//     vis[v] = 1;
//     for (int u : g[v])
//         if (!vis[u])
//             print(u);
//         else if (u == 3)
//             cout << "edge with 3, " << v << endl;
// }

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

    int n, m;
    scanf("%d %d", &n, &m);

    for (int i=1; i<=n; i++){
        par1[i] = par2[i] = -1;
        mnh[i] = n + 100;
        h[i] = n + 100;
    }

    for (int i=0; i<m; i++){
        int u, v;
        scanf("%d %d", &u, &v);

        edges++;
        g[u].push_back({v, edges});
        g[v].push_back({u, edges});

        // if (root1(u) != root1(v))
        //     merge1(u, v);
        // else if (root2(u) != root2(v))
        //     merge2(u, v);
    }


    // cout << " ----------- \n";
    // for (int v = 1; v <= n; v++)
    //     for (int u : g[v])
    //         if (v < u)
    //         cout << v << " " << u << endl;
    // cout << " ----------- \n";

    for (int v = 1; v <= n; v++){
        if (!vis[v]){
            // cout << "---------------\n";
            dfs(v);
        }
    }
    for (int i=1; i<=n; i++)
        vis[i] = 0;

    // printf("------ \n");
    // vis[3] = 1;
    // print(59);
    // printf("------ \n");

    // int cur = 59;
    // while (par[cur]){
    //     cout << cur << " ";
    //     cur = par[cur];
    // }
    // cout << cur << endl;

    for (auto [u, v] : bridges)
        printf("%d %d\n", u, v);
}

/*

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

const int N = 1e5 + 10;
int par1[N], par2[N], h[N], mnh[N];
bool vis[N];
vector<int> g[N];
vector<pair<int, int>> bridges;

int root1(int v){
    return (par1[v] == -1 ? v : par1[v] = root1(par1[v]));
}

int root2(int v){
    return (par2[v] == -1 ? v : par2[v] = root2(par2[v]));
}

void merge1(int u, int v){    
    int r1 = root1(v);
    int r2 = root1(u);

    par1[r1] = r2;

    g[v].push_back(u);
    g[u].push_back(v);
}

void merge2(int u, int v){
    int r1 = root2(u);
    int r2 = root2(v);

    if (r1 == r2)
        return;

    par2[r1] = r2;

    g[v].push_back(u);
    g[u].push_back(v);
}

void dfs(int v, int p = -1){
    vis[v] = 1;
    mnh[v] = h[v];
    for (int u : g[v]){
        if (vis[u]){
            if (u != p)
                mnh[v] = min(mnh[v], h[u]);
            continue;
        }

        h[u] = h[v] + 1;
        dfs(u, v);
        mnh[v] = min(mnh[v], mnh[u]);

        if (mnh[u] >= h[u])
            bridges.push_back({u, v});
    }
}

int main(){
    int n, m;
    scanf("%d%d", &n, &m);

    for (int i=1; i<=n; i++)
        par1[i] = par2[i] = -1;

    for (int i=0; i<m; i++){
        int u, v;
        scanf("%d%d", &u, &v);

        if (root1(u) == root1(v))
            merge2(u, v);
        else
            merge1(u, v);
    }

    for (int v = 1; v <= n; v++)
        if (!vis[v])
            dfs(v);

    for (auto [u, v] : bridges)
        printf("%d %d\n", u, v);
}

*/

Compilation message (stderr)

pipes.cpp: In function 'int main()':
pipes.cpp:90:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   90 |     scanf("%d %d", &n, &m);
      |     ~~~~~^~~~~~~~~~~~~~~~~
pipes.cpp:100:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  100 |         scanf("%d %d", &u, &v);
      |         ~~~~~^~~~~~~~~~~~~~~~~

• Subtask 1: 10 / 10
• Subtask 2: 10 / 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