Submission #94397

#	Time	Username	Problem	Language	Result	Execution time	Memory
94397		gumball	Network (BOI15_net)	C++14	0 / 100	7 ms	7544 KiB

net

#include<bits/stdc++.h>
#define ll long long
#define pb push_back
#define mp make_pair
#define fi first
#define se second
using namespace std;
ll n,m,i,ta,tb,D[101010],daun,bes[101010],ROOT,j,P[101010],sudah[101010],sisa,kel[101010],L[101010];
vector<ll> v[101010],C,w[101010],isi[101010];
vector<pair<pair<ll,ll> ,ll> > Z;
void dfs(ll aa,ll bb)
{
	//cout<<aa<<" "<<bb<<" "<<cc<<"\n";
	bes[aa]=0;
	if(D[aa]==1)bes[aa]=1;
	ll ii;
	for(ii=0;ii<v[aa].size();ii++)
		if(v[aa][ii]!=bb)
		{
			P[v[aa][ii]]=aa;
			dfs(v[aa][ii],aa);
			bes[aa]+=bes[v[aa][ii]];
		}
}
void dfs2(ll aa,ll bb,ll cc,ll dd)
{
	L[aa]=dd;
	if(D[aa]==1)
	{
		kel[dd]++;
		isi[dd].pb(aa);
		Z.pb(mp(mp(cc,dd),aa));
	}
	ll ii;
	for(ii=0;ii<v[aa].size();ii++)
		if(v[aa][ii]!=bb)
			dfs2(v[aa][ii],aa,cc,dd);
}
int main()
{
	//ios_base::sync_with_stdio(NULL);cin.tie(NULL);cout.tie(NULL);
	cin>>n;
	for(i=1;i<n;i++)
	{
		cin>>ta>>tb;
		v[ta].pb(tb);
		v[tb].pb(ta);
		D[ta]++;
		D[tb]++;
	}
	for(i=1;i<=n;i++)
		if(D[i]>1)
			C.pb(i);
		else
			daun++;
	//cout<<daun<<"\n";
	for(i=0;i<C.size();i++)
	{
		vector<ll> X;
		ROOT=C[i];
		//cout<<ROOT<<"\n";
		dfs(ROOT,ROOT);		
		for(j=0;j<v[ROOT].size();j++)
			X.pb(bes[v[ROOT][j]]);
		//return 0;
		sort(X.begin(),X.end());
		reverse(X.begin(),X.end());
		if(X[0]*2<=daun)
			break;
		else
			ROOT=-1;
	}
	if(ROOT==-1)while(1);
	//cout<<ROOT<<"\n";
	//return 0;
	for(i=0;i<v[ROOT].size();i++)
		dfs2(v[ROOT][i],ROOT,bes[v[ROOT][i]],i);
	cout<<(daun/2+daun%2)<<"\n";
	sort(Z.begin(),Z.end());
	if(daun%2==1)
	{
		if(P[Z[daun-1].se]!=ROOT)cout<<Z[daun-1].se<<" "<<ROOT<<"\n";
		else
		{
			for(i=1;i<=n;i++)
				if(L[i]!=L[Z[daun-1].se])
				{
					cout<<Z[daun-1].se<<" "<<i<<"\n";
					break;
				}
		}
		daun--;
		kel[Z[daun-1].fi.se]--;
		Z.pop_back();
	}
	sisa=daun/2;
	for(i=0;i<(daun/2);i++)
	{
		vector<pair<ll,ll> > B;
	//	cout<<i<<"\n";
		for(j=0;j<v[ROOT].size();j++)
			B.pb(mp(-kel[j],j));
		sort(B.begin(),B.end());
		if(B[1].fi==0)while(1);
		cout<<isi[B[0].se].back()<<" "<<isi[B[1].se].back()<<"\n";
		//if(i==1)return 0;
		//return 0;
		kel[B[0].se]--;
		kel[B[1].se]--;
		isi[B[0].se].pop_back();
		isi[B[1].se].pop_back();
	}
	//if(sisa)while(1);
}

Compilation message (stderr)

net.cpp: In function 'void dfs(long long int, long long int)':
net.cpp:17:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(ii=0;ii<v[aa].size();ii++)
           ~~^~~~~~~~~~~~~
net.cpp: In function 'void dfs2(long long int, long long int, long long int, long long int)':
net.cpp:35:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(ii=0;ii<v[aa].size();ii++)
           ~~^~~~~~~~~~~~~
net.cpp: In function 'int main()':
net.cpp:57:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=0;i<C.size();i++)
          ~^~~~~~~~~
net.cpp:63:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(j=0;j<v[ROOT].size();j++)
           ~^~~~~~~~~~~~~~~
net.cpp:76:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=0;i<v[ROOT].size();i++)
          ~^~~~~~~~~~~~~~~
net.cpp:101:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(j=0;j<v[ROOT].size();j++)
           ~^~~~~~~~~~~~~~~

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