Submission #1142878

#	Time	Username	Problem	Language	Result	Execution time	Memory
1142878		dpsaveslives	Network (BOI15_net)	C++20	100 / 100	198 ms	60868 KiB

net

#include <bits/stdc++.h>
using namespace std;
const int MAXN = 5e5+5;
vector<int> adj[MAXN];
vector<int> deg,leaf;
void dfs(int u, int p){
    if(deg[u] == 1){
        leaf.push_back(u);
        return;
    }
    for(auto v : adj[u]){
        if(v != p){
            dfs(v,u);
        }
    }
}
int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    int N; cin >> N;
    deg = vector<int>(N+1,0);
    for(int i = 0;i<=N-2;++i){
        int u,v; cin >> u >> v;
        adj[u].push_back(v); adj[v].push_back(u);
        ++deg[u]; ++deg[v];
    }
    int root = 1;
    for(int i = 1;i<=N;++i){
        if(deg[i] >= 2){
            root = i;
        }
    }
    dfs(root,0);
    vector<pair<int,int>> ans;
    for(int i = 0;i<=(leaf.size()/2)-1;++i){
        ans.push_back({leaf[i],leaf[i+leaf.size()/2]});
    }
    if(leaf.size() % 2 == 1){
        ans.push_back({leaf[0],leaf[leaf.size()-1]});
    }
    cout << ans.size() << "\n";
    for(auto x : ans){
        cout << x.first << " " << x.second << "\n";
    }
    return 0;
}

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