Submission #900101

#	Time	Username	Problem	Language	Result	Execution time	Memory
900101		LCJLY	Network (BOI15_net)	C++14	0 / 100	4 ms	13692 KiB

net

#include <bits/stdc++.h>
using namespace std;

#define int long long
#define ld long double
#define show(x,y) cout << y << " " << #x << endl;
#define show2(x,y,i,j) cout << y << " " << #x << "  " << j << " " << #i << endl;
#define show3(x,y,i,j,p,q) cout << y << " " << #x << "  " << j << " " << #i << "  " << q << " " << #p << endl; 
#define show4(x,y) for(auto it:x) cout << it << " "; cout << #y << endl;
typedef pair<long long,long long>pii;
typedef pair<pii,pii>pi2;

vector<int>adj[500005];
int dist[500005];
int dist2[500005];

void dfs(int index, int par, int d[]){
	for(auto it:adj[index]){
		if(it==par) continue;
		d[it]=d[index]+1;
		dfs(it,index,d);
	}
}

void solve(){	
	int n;
	cin >> n;
	
	int temp,temp2;
	for(int x=0;x<n-1;x++){
		cin >> temp >> temp2;
		adj[temp].push_back(temp2);
		adj[temp2].push_back(temp);
	}
	
	dfs(1,-1,dist);
	int maxi=0;
	int a=1;

	for(int x=1;x<=n;x++){
		if(dist[x]>maxi){
			maxi=dist[x];
			a=x;
		}
	}
	
	dist[a]=0;
	dfs(a,-1,dist);

	int b=a;
	maxi=0;
	
	for(int x=1;x<=n;x++){
		if(dist[x]>maxi){
			maxi=dist[x];
			b=x;
		}
	}
	
	vector<int>leaf;
	for(int x=1;x<=n;x++){
		if(adj[x].size()==1){
			if(x==a||x==b) continue;
			leaf.push_back(x);
		}
	}
	
	vector<pii>ans;
	ans.push_back({a,b});
	
	if((int)leaf.size()%2==1){
		ans.push_back({leaf.back(),a});
		leaf.pop_back();
	}
	
	for(int x=1;x<(int)leaf.size();x+=2){
		ans.push_back({leaf[x],leaf[x-1]});
	}
	
	cout << ans.size() << "\n";
	for(auto it:ans){
		cout << it.first << " " << it.second << "\n";
	}
}	

int32_t main(){										
	ios::sync_with_stdio(0);	
	cin.tie(0);
	int t=1;
	//cin >> t;
	while(t--){
		solve();
	}
}

		

• Subtask 1: 0 / 18
• Subtask 2: 0 / 45
• Subtask 3: 0 / 37