Submission #851050

#	Time	Username	Problem	Language	Result	Execution time	Memory
851050		emkow	Network (BOI15_net)	C++17	0 / 100	1 ms	600 KiB

net

#include <bits/stdc++.h>
#pragma GCC optimize("O3", "unroll-loops")
#define pb emplace_back
#define ins insert
#define ssize(x) (int)x.size()
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define pii pair <int, int>
#define pll pair <ll, ll>
#define pld pair <ld, ld>
#define st first
#define nd second

using namespace std;
using ll = int_fast64_t;
// using lll = __int128_t;
using ld = long double;
const int oo = 1e9 + 7;
const int mod = 1e9 + 7;

void solve(){
    int n; cin >> n;
    vector <int> deg(n, 0);
    for(int i = 1; i < n; i ++){
        int a, b; cin >> a >> b;
        -- a; -- b;
        deg[a] ++;
        deg[b] ++;
    }
    vector <int> leaves;
    for(int i = 0; i < n; i ++){
        if(deg[i] == 1) leaves.pb(i);
    }
    cout << (ssize(leaves) + 1) / 2 << '\n';
    for(int i = 0; i < ssize(leaves) / 2; i ++){
        cout << leaves[i] + 1 << ' ' << leaves[i + ssize(leaves) / 2] + 1 << '\n';
    }
    if(ssize(leaves) & 1) cout << leaves[0] + 1 << ' ' << leaves.back() + 1 << '\n';
}

signed main(){
    ios_base::sync_with_stdio(0); cin.tie(0);
    int t; t = 1;
    // cin >> t;
    while(t --) solve();
    return 0;
}

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