Submission #395013

#	Time	Username	Problem	Language	Result	Execution time	Memory
395013		soroush	Network (BOI15_net)	C++17	100 / 100	491 ms	63428 KiB

net

//曇り空 のぞいた予感
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef long double ld;
typedef pair<int , int> pii;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

const int maxn = 5e5 + 100;
const ll mod = 1e9+7;

#define pb push_back
#define endl '\n'
#define dokme(x) cout << x , exit(0)
#define ms(x , y) memset(x , y , sizeof x)
ll pw(ll a, ll b, ll md = mod){ll res = 1;while(b){if(b&1){res=(a*res)%md;}a=(a*a)%md;b>>=1;}return(res);}

#define sz(x) int(x.size())

int n;
vector < int > adj[maxn] , leaf;

void dfs(int v , int par = 0){
	for(auto u : adj[v])if(u ^ par)
		dfs(u , v);
	if(sz(adj[v]) == 1)leaf.pb(v);
}

int32_t main(){
	ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
	cin >> n;
	int root;
	for(int i = 1 ; i < n ; i ++){
		int u , v;
		cin >> u >> v;
		adj[u].pb(v);
		adj[v].pb(u);
	}
	for(int i = 1 ; i <= n ; i ++)	
		if(sz(adj[i]) > 1)root = i;
	dfs(root);
	cout << (sz(leaf)+1)/2 << endl;
	for(int i = 0 ; i < (sz(leaf)+1)/2 ; i ++)
		cout << leaf[i] << ' ' << leaf[i + sz(leaf)/2] << endl;
	return(0);
}

Compilation message (stderr)

net.cpp: In function 'int32_t main()':
net.cpp:44:5: warning: 'root' may be used uninitialized in this function [-Wmaybe-uninitialized]
   44 |  dfs(root);
      |  ~~~^~~~~~

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