Submission #606815

#	Time	Username	Problem	Language	Result	Execution time	Memory
606815		ThMinh_	Network (BOI15_net)	C++14	100 / 100	672 ms	239644 KiB

net

#include<bits/stdc++.h>
#define forin(i,a,b) for(int i=a;i<=b;++i)
#define forv(a,b) for(auto &a:b)
#define ii pair<int, int>
using namespace std;
const int N = 5e5+10;
int n, root;
int color[N];
vector<int> adj[N];
vector<ii> ans;
queue<int> dfs(int u) {
	color[u] = 1;
	queue<int> res;
	if(adj[u].size() == 1) {res.push(u); return res;}
	forv(v, adj[u]) if(!color[v]) {
		queue<int> q = dfs(v);
		if(res.size() + q.size() > 2 && res.size() > 0 && q.size() > 0) {
			ans.push_back({res.front(), q.front()});
			res.pop(); q.pop();
		}
		while(!q.empty()) {res.push(q.front()); q.pop();}
	}
	return res;
}
int main () {
	cin.tie(0)->sync_with_stdio(0);
	if(fopen("Task.inp","r")) {
		freopen("Task.inp","r",stdin);
		freopen("WA.out","w",stdout);
	}
	cin>>n;
	forin(i,1,n - 1) {
		int u, v; cin>>u>>v;
		adj[u].push_back(v);
		adj[v].push_back(u);
	}
	queue<int> slt;
	forin(i,1,n) if(adj[i].size() > 1) {slt = dfs(i); root = i; break;}
	if(slt.size() == 2) {root = slt.front(); slt.pop();}
	if(slt.size() == 1) ans.push_back({root, slt.front()});
	cout<<ans.size()<<"\n";
	forv(v, ans) cout<<v.first<<" "<<v.second<<"\n";
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:28:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   28 |   freopen("Task.inp","r",stdin);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
net.cpp:29:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   29 |   freopen("WA.out","w",stdout);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~

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