Submission #394603

#	Time	Username	Problem	Language	Result	Execution time	Memory
394603		AmShZ	Network (BOI15_net)	C++11	100 / 100	641 ms	51392 KiB

net

// khodaya khodet komak kon
// Toxicity
# include <bits/stdc++.h>

using namespace std;

typedef long long                                        ll;
typedef long double                                      ld;
typedef pair <int, int>                                  pii;
typedef pair <pii, int>                                  ppi;
typedef pair <int, pii>                                  pip;
typedef pair <pii, pii>                                  ppp;
typedef pair <ll, ll>                                    pll;

# define A                                               first
# define B                                               second
# define endl                                            '\n'
# define sep                                             ' '
# define all(x)                                          x.begin(), x.end()
# define kill(x)                                         return cout << x << endl, 0
# define SZ(x)                                           int(x.size())
# define lc                                              id << 1
# define rc                                              id << 1 | 1
# define InTheNameOfGod                                  ios::sync_with_stdio(0);cin.tie(0); cout.tie(0);

ll power(ll a, ll b, ll md) {return (!b ? 1 : (b & 1 ? a * power(a * a % md, b / 2, md) % md : power(a * a % md, b / 2, md) % md));}

const int xn = 5e5 + 10;
const int xm = - 20 + 10;
const int sq = 320;
const int inf = 1e9 + 10;
const ll INF = 1e18 + 10;
const int mod = 998244353;
const int base = 257;

int n, sz[xn], root, m, a[xn];
vector <int> adj[xn];

void plant(int v, int p = - 1){
	sz[v] = 1;
	for (int u : adj[v])
		if (u != p)
			plant(u, v), sz[v] += sz[u];
}
int find_centroid(int v, int p = - 1){
	for (int u : adj[v])
		if (u != p && sz[u] + sz[u] > n)
			return find_centroid(u, v);
	return v;
}
void DFS(int v, int p = - 1){
	if (SZ(adj[v]) == 1)
		a[m ++] = v;
	for (int u : adj[v])
		if (u != p)
			DFS(u, v);
}

int main(){
	InTheNameOfGod;

	cin >> n;
	for (int i = 0; i < n - 1; ++ i){
		int v, u;
		cin >> v >> u;
		adj[v].push_back(u);
		adj[u].push_back(v);
	}
	plant(1);
	root = find_centroid(1);
	DFS(root);
	cout << (m + 1) / 2 << endl;
	for (int i = 0; i < (m + 1) / 2; ++ i)
		cout << a[i] << sep << a[i + m / 2] << endl;

	return 0;
}

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