Submission #1173401

#	Time	Username	Problem	Language	Result	Execution time	Memory
1173401		InvMOD	Network (BOI15_net)	C++20	100 / 100	357 ms	53848 KiB

net

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

#define fi first
#define se second
#define gcd __gcd
#define sz(v) (int) v.size()
#define pb push_back
#define pi pair<int,int>
#define all(v) (v).begin(), (v).end()
#define compact(v) (v).erase(unique(all(v)), (v).end())
#define FOR(i, a, b) for(int i = (a); i <= (b); i++)
#define REV(i, a, b) for(int i = (a); i >= (b); i--)
#define dbg(x) "[" #x " = " << (x) << "]"
///#define int long long

using ll = long long;
using ld = long double;
using ull = unsigned long long;

template<typename T> bool ckmx(T& a, const T& b){if(a < b) return a = b, true; return false;}
template<typename T> bool ckmn(T& a, const T& b){if(a > b) return a = b, true; return false;}

const int N = 2e5+5;
const ll MOD = 1e9+7;
const ll INF = 1e18;


void solve()
{
    int n; cin >> n;

    vector<vector<int>> adj(n + 1, vector<int>());
    for(int i = 1; i < n; i++){
        int u,v; cin >> u >> v;
        adj[u].pb(v), adj[v].pb(u);
    }

    vector<int> leaf;
    function<void(int,int)> preDFS = [&](int x, int p) -> void{
        if(sz(adj[x]) == 1) leaf.push_back(x);
        for(int v : adj[x])if(v != p){
            preDFS(v, x);
        }
    };
    preDFS(1, -1);

    cout << sz(leaf) / 2 + (sz(leaf) & 1) << "\n";
    for(int i = 0; i < sz(leaf) / 2; i++){
        cout << leaf[i] << " " << leaf[i + sz(leaf) / 2] << "\n";
    }
    if(sz(leaf) & 1){
        cout << leaf.back() <<" " << leaf[0] << "\n";
    }

    cout << "\n";
}

signed main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    #define name "InvMOD"
    if(fopen(name".INP", "r")){
        freopen(name".INP","r",stdin);
        freopen(name".OUT","w",stdout);
    }

    int t = 1; //cin >> t;
    while(t--) solve();
    return 0;
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:67:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   67 |         freopen(name".INP","r",stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
net.cpp:68:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   68 |         freopen(name".OUT","w",stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~

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