Submission #922723

#	Time	Username	Problem	Language	Result	Execution time	Memory
922723		Alihan_8	Network (BOI15_net)	C++17	100 / 100	438 ms	47056 KiB

net

#include <bits/stdc++.h>

using namespace std;

#define all(x) x.begin(), x.end()
#define ar array
#define pb push_back
#define ln '\n'
#define int long long

using i64 = long long;

template <class F, class _S>
bool chmin(F &u, const _S &v){
    bool flag = false;
    if ( u > v ){
        u = v; flag |= true;
    }
    return flag;
}

template <class F, class _S>
bool chmax(F &u, const _S &v){
    bool flag = false;
    if ( u < v ){
        u = v; flag |= true;
    }
    return flag;
}

signed main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int n; cin >> n;

    vector <vector<int>> G(n);

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

    vector <int> lf;

    auto dfs = [&](auto dfs, int u, int p) -> void{
        for ( auto &v: G[u] ){
            if ( v != p ){
                dfs(dfs, v, u);
            }
        }
        if ( G[u].size() == 1 ){
            lf.pb(u);
        }
    };

    dfs(dfs, 0, -1);

    if ( lf.size() & 1 ){
        lf.pb(lf[0]);
    }

    int k = lf.size();
    cout << k / 2 << ln;
    for ( int i = 0; i * 2 < k; i++ ){
        cout << lf[i] + 1 << ' ' << lf[i + k / 2] + 1 << ln;
    }

    cout << '\n';
}

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