제출 #1179933

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
1179933		nguyenkhangninh99	Network (BOI15_net)	C++20	0 / 100	34 ms	70728 KiB

net

#include <bits/stdc++.h>

using namespace std;

#define pii pair<int, int>
#define fi first
#define se second

const int maxn = 1e6 + 5;

int low[maxn], num[maxn], compid[maxn];
int timeDfs = 0, scc = 0;

vector<int> g[maxn];
set<int> adj[maxn];

stack<int> s;

void dfs2(int u, int pre){
    low[u] = num[u] = ++timeDfs;
    s.push(u);
    for (int v: g[u]){
        if (v != pre){
            if (!num[v]){
                dfs2(v, u);
                low[u] = min(low[u], low[v]);
            }
            else low[u] = min(low[u], num[v]);
        }
    }

    if (low[u] == num[u]){
        while(true){
            int v = s.top();
            s.pop();
            compid[v] = u;
            if(v == u) break;
        }
    }
}

void solve (){
    int n; cin >> n;

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

    dfs2(1, -1);

    for(int u = 1; u <= n; u++){
        for (int v: g[u]){
            if (compid[u] != compid[v]){
                adj[compid[u]].insert(compid[v]);
                adj[compid[v]].insert(compid[u]);
            }
        }
    }

    int ans = 0;
    vector<int> v;

    for(int i = 1; i <= n; i++){
        if(adj[i].size() == 1){
            ans++;
            v.push_back(i);
        }
    }

    cout << (ans + 1) / 2 << "\n";
    if(v.size() % 2 == 1) cout << 1 << " " << v.back() << "\n";
    for(int i = 0; i + 1 < v.size(); i += 2){
        cout << v[i] << " " << v[i + 1] << "\n";
    }

}

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

    solve();
}

• Subtask 1: 0 / 18
• Subtask 2: 0 / 45
• Subtask 3: 0 / 37