Submission #1142463

#	Time	Username	Problem	Language	Result	Execution time	Memory
1142463		thelegendary08	Network (BOI15_net)	C++17	100 / 100	220 ms	62768 KiB

net

#include<bits/stdc++.h>
#define pb push_back
#define mp make_pair
#define int long long
#define vi vector<int>
#define vvi vector<vector<int>>
#define pii pair<int, int>
#define vpii vector<pair<int, int>>
#define vc vector<char>
#define vb vector<bool>
#define mii map<int,int>
#define f0r(i,n) for(int i=0;i<n;i++)
#define FOR(i,k,n) for(int i=k;i<n;i++)
#define all(v) (v).begin(),(v).end()
#define rall(v) (v).rbegin(),(v).rend()
#define in(a) int a; cin>>a
#define in2(a,b) int a,b; cin>>a>>b
#define in3(a,b,c) int a,b,c; cin>>a>>b>>c
#define in4(a,b,c,d) int a,b,c,d; cin>>a>>b>>c>>d
#define vin(v,n); vi v(n); f0r(i,n){cin>>v[i];}
#define out(a) cout<<a<<'\n'
#define out2(a,b) cout<<a<<' '<<b<<'\n'
#define out3(a,b,c) cout<<a<<' '<<b<<' '<<c<<'\n'
#define out4(a,b,c,d) cout<<a<<' '<<b<<' '<<c<<' '<<d<<'\n'
#define pout(a) cout<<a.first<<' '<<a.second<<'\n'
#define vout(v) for(auto u : v){cout<<u<<' ';} cout<<'\n'
#define dout(a) cout<<a<<' '<<#a<<'\n'
#define dout2(a,b) cout<<a<<' '<<#a<<' '<<b<<' '<<#b<<'\n'
#define yn(x); if(x){cout<<"YES"<<'\n';}else{cout<<"NO"<<'\n';}
const int leg = 1e9 + 7;
const int mod = 998244353;
using namespace std;
const int mxn = 5e5 + 5;
vi deg(mxn);
vi leaves;
vi adj[mxn];
void dfs(int node, int from){
	if(deg[node] == 1){
		leaves.pb(node);
	}
	for(auto u : adj[node]){
		if(u != from){
			dfs(u, node);
		}
	}
}
signed main(){
	ios::sync_with_stdio(false);
	cin.tie(NULL);
	//ifstream cin(".in");
	//ofstream cout(".out");
	in(n);
	f0r(i,n-1){
		in2(a,b);
		a--; b--;
		adj[a].pb(b);
		adj[b].pb(a);	
		deg[a]++;
		deg[b]++;
	}
	int root = -1;
	f0r(i,n){
		if(deg[i] >= 2)root = i;
	}
	dfs(root,-1);
	vpii ans;
	for(int i = 0; i<leaves.size()/2; i++){
		ans.pb(mp(leaves[i], leaves[i+leaves.size() / 2]));
	}
	if(leaves.size() % 2 == 1){
		ans.pb(mp(leaves[0], leaves[leaves.size() - 1]));
	}
	out(ans.size());
	for(auto u : ans){
		out2(u.first+1, u.second+1);
	}
}

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