Submission #978022

#	Time	Username	Problem	Language	Result	Execution time	Memory
978022		AlphaMale06	Network (BOI15_net)	C++17	100 / 100	374 ms	59632 KiB

net

#include <bits/stdc++.h>

using namespace std;

#define pb push_back

const int N = 5e5+3;
int deg[N];
vector<int> g[N];
vector<int> ls;

void dfs(int v, int p){
    if(g[v].size()==1)ls.pb(v);
    for(int to : g[v]){
        if(to!=p)dfs(to, v);
    }
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int n;
    cin >> n;
    for(int i=1; i<n; i++){
        int a, b;
        cin >> a >> b;
        g[a].pb(b);
        g[b].pb(a);
        deg[a]++;
        deg[b]++;
    }
    int root=1;
    for(int i=2; i<=n; i++){
        if(deg[i]>1)root=i;
    }
    dfs(root, root);
    int cnt=ls.size();
    cout << (cnt+1)/2 << '\n';
    for(int i=0; i<cnt/2; i++){
        cout << ls[i] << " " << ls[i+cnt/2] << '\n';
    }
    if(cnt&1)cout << ls[0] << " " << ls.back() << '\n';
}

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