Submission #94406

#	Time	Username	Problem	Language	Result	Execution time	Memory
94406		gumball	Network (BOI15_net)	C++14	100 / 100	921 ms	128296 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[501010],daun,bes[501010],ROOT,j,P[501010],sudah[501010],sisa,kel[501010],L[501010],VS;
vector<ll> v[501010],C,w[501010],isi[501010];
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,ma=0;
	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]];
			ma=max(ma,bes[v[aa][ii]]);
		}
	}
	ma=max(ma,daun-bes[aa]);
	//cout<<aa<<" "<<ma<<"\n";
	if(ma*2<=daun)ROOT=aa;
}
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";
	dfs(C[0],C[0]);	
	//cout<<ROOT<<"\n";
	//return 0;
	VS=v[ROOT].size();
	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)
	{
		ll OO=Z[daun-1].fi.se;
		if(isi[OO].back()!=ROOT)cout<<isi[OO].back()<<" "<<ROOT<<"\n";
		else
		{
			for(i=1;i<=n;i++)
				if(L[i]!=L[isi[OO].back()])
				{
					cout<<isi[OO].back()<<" "<<i<<"\n";
					break;
				}
		}
		daun--;
		kel[OO]--;
		isi[OO].pop_back();
		Z.pop_back();
	}
	priority_queue<pair<ll,ll> > pq;
	sisa=daun/2;
	for(i=0;i<VS;i++)pq.push(mp(kel[i],i));
	for(i=0;i<(daun/2);i++)
	{
		while(kel[pq.top().se]!=pq.top().fi)pq.pop();
		ll A=pq.top().se;
		pq.pop();
		ll B=pq.top().se;
		pq.pop();
		cout<<isi[A].back()<<" "<<isi[B].back()<<"\n";
		kel[A]--;
		kel[B]--;
		isi[A].pop_back();
		isi[B].pop_back();
		pq.push(mp(kel[A],A));
		pq.push(mp(kel[B],B));
	}
	//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:41:13: 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:67:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(i=0;i<v[ROOT].size();i++)
          ~^~~~~~~~~~~~~~~

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