Submission #394663

#	Time	Username	Problem	Language	Result	Execution time	Memory
394663		saniyar_krmi	Network (BOI15_net)	C++14	100 / 100	645 ms	64284 KiB

net

// Possible Overdose for this coder
#include <bits/stdc++.h>
#define put(x) cerr << #x << ": " << x << '\n'
#define line() cerr << "**************\n"

//#define F first
//#define S second
//#define mul(x, y) (((x) * (y)) %mod)
//#define bit(i, j) (((i)>>(j)) &1)
//#define left(id) ((id<<1) + 1)
//#define right(id) ((id<<1) + 2)
 
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<pii, int> piii;

const int maxn = 5e5 + 10;
int n;
vector <int> G[maxn];
int l[maxn], num;

void dfs(int v, int par){
	if(G[v].size() == 1)
		l[v] = 1;

	for(int u: G[v]){
		if(u == par)
			continue;
		dfs(u, v);
		l[v] += l[u];
	}
}

int find(int v, int par){
	for(int u: G[v]){
		if(u == par)
			continue;
		if(l[u] > num / 2)
			return find(u, v);
	}
	return v;
}

vector <int> s[maxn];
void make(int v, int par, int x){
	if(G[v].size() == 1)
		s[x].push_back(v);

	for(int u: G[v]){
		if(u == par)
			continue;
		make(u, v, x);
	}
}

int main(){
	ios_base::sync_with_stdio(false);
	cin.tie(0);  cout.tie(0);

	cin >> n;
	int u, v;
	for(int i=1; i<n; i++){
		cin >> u >> v;
		G[u].push_back(v), G[v].push_back(u);
	}

	dfs(1, 0);
	num = l[1];

	v = find(1, 0);

	int cnt = 0;
	for(int u: G[v])
		make(u, v, cnt++);

	int res = (num + 1) >> 1;
	vector <int> ans(2 * res);
	
	int pt = 0;
	for(int i=0; i<cnt; i++)
		for(int vi: s[i]){
			ans[pt] = vi;
			pt += 2;
			if(pt == (2 * res))
				pt = 1;
		}
	
	if(ans.size() && ans.back() == 0)
		ans.back() = s[0][0], put(1);

	cout << res << '\n';
	for(int i=0; i<ans.size(); i+=2)
		cout << ans[i] << ' ' << ans[i + 1] << '\n';
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:94:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   94 |  for(int i=0; i<ans.size(); i+=2)
      |               ~^~~~~~~~~~~

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