Submission #96949

#	Time	Username	Problem	Language	Result	Execution time	Memory
96949		dalgerok	Network (BOI15_net)	C++14	100 / 100	750 ms	65728 KiB

net

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


const int N = 5e5 + 5;



int n, sz, a[N];
vector < int > g[N];

void dfs(int v, int pr = -1){
    for(int to : g[v]){
        if(to != pr){
            dfs(to, v);
        }
    }
    if((int)g[v].size() == 1){
        a[++sz] = v;
    }
}

int main(){
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    cin >> n;
    for(int i = 1; i < n; i++){
        int x, y;
        cin >> x >> y;
        g[x].push_back(y);
        g[y].push_back(x);
    }
    int rt = -1;
    for(int i = 1; i <= n; i++){
        if((int)g[i].size() > 1){
            rt = i;
        }
    }
    dfs(rt);
    int ans = (sz + 1) / 2;
    cout << ans << "\n";
    for(int i = 1; i < ans; i++){
        cout << a[i] << " " << a[i + ans] << "\n";
    }
    if(sz & 1){
        cout << a[1] << " " << a[ans] << "\n";
    }
    else{
        cout << a[sz] << " " << a[ans];
    }
}

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