Submission #519928

#	Time	Username	Problem	Language	Result	Execution time	Memory
519928		Hacv16	Network (BOI15_net)	C++17	100 / 100	481 ms	82996 KiB

net

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

typedef long long ll;
typedef pair<int, int> pii;

const int MAX = 2e6 + 15;
const int INF = 0x3f3f3f3f;
const int MOD = 1e9 + 7;

#define pb push_back
#define sz(x) (int) x.size()
#define fr first
#define sc second
#define mp make_pair
#define all(x) x.begin(), x.end()
#define dbg(x) cout << #x << ": " << "[ " << x << " ]\n"

int n;
vector<int> adj[MAX], l;

void setIO(){
    ios_base::sync_with_stdio(false);
    cin.tie(NULL); 
}

void dfs(int x, int p){
    if(sz(adj[x]) == 1){
        l.pb(x);
    }

    for(auto v : adj[x]){
        if(v == p) continue;
        dfs(v, x);
    }
}

int main(){
    setIO();

    cin >> n;

    for(int i = 1; i < n; i++){
        int u, v; cin >> u >> v;

        adj[u].pb(v);
        adj[v].pb(u);
    }

    dfs(1, -1);

    int e = sz(l) / 2 + (sz(l) % 2);

    cout << e << '\n';

    for(int i = 0; i < e; i++){
        int u = l[i], v = (i + sz(l)/2 < sz(l) ? l[i + sz(l)/2] : l[0]);
        cout << u << ' ' << v << '\n';
    }

    return 0;
}

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