Submission #996973

#	Time	Username	Problem	Language	Result	Execution time	Memory
996973		underwaterkillerwhale	Network (BOI15_net)	C++17	100 / 100	240 ms	51660 KiB

net

#include <bits/stdc++.h>
#define se              second
#define fs              first
#define mp              make_pair
#define pb              push_back
#define ll              long long
#define ii              pair<ll,ll>
#define ld              long double
#define SZ(v)           (int)v.size()
#define ALL(v)          v.begin(), v.end()
#define bit(msk, i)     ((msk >> i) & 1)
#define iter(id, v)     for(auto id : v)
#define rep(i,m,n)      for(int i=(m); i<=(n); i++)
#define reb(i,m,n)      for(int i=(m); i>=(n); i--)

using namespace std;

mt19937_64 rd(chrono :: steady_clock :: now().time_since_epoch().count());
ll Rand(ll l, ll r) { return uniform_int_distribution<ll> (l, r)(rd); }

const int N  = 5e5 + 7;
const int Mod = 998244353;
const int szBL = 916;
const ll INF = 1e18;
const int BASE = 137;

int n;
vector<int> ke[N];

int in[N], out[N];

vector<int> leaves;
vector<pair<int,int>> Ans;

void pdfs (int u, int p) {
    static int time_dfs = 0;
    if (SZ(ke[u]) <= 1) {
        leaves.push_back(u);
    }
    in[u] = ++time_dfs;
    iter (&v, ke[u]) {
        if (v != p) pdfs (v, u);
    }
    out[u] = time_dfs;
}

void solution () {
    cin >> n;
    rep (i, 1, n - 1) {
        int u, v;
        cin >> u >> v;
        ke[u].push_back(v);
        ke[v].push_back(u);
    }
    pdfs (1, 0);
    cout << (SZ(leaves) + 1) / 2 <<"\n";
    rep (i, 0, SZ(leaves) / 2 - 1) {
        cout << leaves[i] <<" "<<leaves[i + SZ(leaves) / 2] <<"\n";
    }
    if (SZ(leaves) & 1) cout << leaves.back()<< " "<<leaves[0]<<"\n";

}
#define file(name) freopen(name".inp", "r", stdin); freopen(name".out", "w", stdout);
int main () {
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

//    file ("fbuy");
    int num_Test = 1;
//    cin >> num_Test;
    while (num_Test--)
        solution();
}
/*
7
1 2 4
2 3 12
3 4 2
4 5 48
5 6 2
6 7 123

*/

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