Submission #397314

#	Time	Username	Problem	Language	Result	Execution time	Memory
397314		Bitmasking	Network (BOI15_net)	C++14	100 / 100	452 ms	52880 KiB

net

#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
#define f(i,a,b) for( ll i = a; i < b ; i++ )
#define af(i,a,b) for( ll i = a; i >= b ; i--)
#define rep(i,a,b,k) for(ll i = a; i < b ; i+= k )
#define arep(i,a,b,k) for( ll i = a; i >= b ; i-= k)
#define ones(ini) (ll) __builtin_popcountll(x)
#define todo(y,val) all_of(all(y),[&val](ll x) {return (x == ((ll)val));})
#define nada(y,val) none_of(all(y),[&val](ll x) {return (x == ((ll)val));})
#define algu(y,val) any_of(all(y),[&val](ll x) {return (x == ((ll)val));})
#define cuantos(a,x) count(all(a),x)
#define fs first
#define sc second
#define pb push_back
#define po pop_back
#define sz(a) (ll) a.size()
#define all(a) a.begin(), a.end()
#define sor(a) sort( a.begin(), a.end() )
#define fastio ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0)
#define ller ios::sync_with_stdio(false);cin.tie(nullptr);cout.tie(nullptr)
#define watch(x) cout << (#x) << " is " << (x) <<"\n"
#define test ll deftestcases;cin>>deftestcases;while(deftestcases--)
#define PI acos(-1)
using namespace std;
typedef long long ll;
typedef long double ld; 
typedef pair<ll,ll> ii;
typedef vector<ll>  vi;
typedef vector<ii> vii;
template<class T> using ordered_set =tree<T, null_type, less<T>, rb_tree_tag,tree_order_statistics_node_update> ;
const ll inf = 2e9;
const ll mod = 1e9+7;   
const ll MAX = 5e5+10;
 
vi adj[MAX];
vi hojas;
 
void dfs(ll u,ll par){
    for(auto v : adj[u]){
        if(v!=par) dfs(v,u);
    }
    if(sz(adj[u])==1) hojas.pb(u);
}
 
int main(){
    fastio;
    ll n;cin>>n;
    f(i,0,n-1){
        ll u,v;
        cin>>u>>v;
        adj[u].pb(v);
        adj[v].pb(u);
    }    
    dfs(1,0);
    n = sz(hojas);
    cout<<(n + n%2)/2<<"\n";
    f(i,0,n/2) cout<<hojas[i]<<" "<<hojas[n/2+i]<<"\n";
    if(n&1) cout<<hojas[0]<<" "<<hojas[n-1]<<"\n";
    return 0; 
}

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