Submission #550586

#	Time	Username	Problem	Language	Result	Execution time	Memory
550586		OttoTheDino	Network (BOI15_net)	C++17	100 / 100	428 ms	47704 KiB

net

#include <bits/stdc++.h>
using namespace std;
 
#define rep(i,s,e)                  for (int i = s; i <= e; ++i)
#define rrep(i,s,e)                 for (int i = s; i >= e; --i)
#define pb                          push_back
#define pf                          push_front
#define fi                          first
#define se                          second
#define all(a)                      a.begin(), a.end()
#define SZ(a)                       (int)a.size()
typedef long long ll;
typedef pair<int, int> ii;
typedef vector<ii> vii;
typedef vector<int> vi;
typedef vector<double> vd;
typedef vector<string> vs;
typedef vector<ll> vll;
 
const int mx = 5e5;
vi adj[mx+1], leaves;
int x;
 
void dfs (int u, int p) {
    if (SZ(adj[u])==1) leaves.pb(u);
    else x = u;
    for (int v : adj[u]) {
        if (v==p) continue;
        dfs (v,u);
    }
}
 
int main() {
    ios::sync_with_stdio(0);
    cin.tie(0);
 
    int n; cin >> n;
    rep (i,1,n-1) {
        int u, v; cin >> u >> v;
        adj[u].pb(v);
        adj[v].pb(u);
    }
 
    dfs (1,-1);
 
    int m = leaves.size();
 
    cout << (m+1)/2 << "\n";
 
    rep (i,0,m/2-1) {
        cout << leaves[i] << " " << leaves[i+m/2] << "\n";
    }
 
    if (m%2) cout << leaves[m-1] << " " << leaves[m/2] << "\n";
 
    return 0;
}
 

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