#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];
vector<ll> v[101010],C,w[101010];
vector<pair<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)
{
if(D[aa]==1)Z.pb(mp(cc,aa));
ll ii;
for(ii=0;ii<v[aa].size();ii++)
if(v[aa][ii]!=bb)
dfs2(v[aa][ii],aa,cc);
}
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;
}
//cout<<ROOT<<"\n";
//return 0;
for(i=0;i<v[ROOT].size();i++)
dfs2(v[ROOT][i],ROOT,bes[v[ROOT][j]]);
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=0;i<C.size();i++)
if(P[Z[daun-1].se]!=C[i])
{
cout<<Z[daun-1].se<<" "<<C[i]<<"\n";
break;
}
}
daun--;
}
for(i=0;i<(daun/2);i++)
cout<<Z[daun-1-i].se<<" "<<Z[i].se<<"\n";
}
Compilation message
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)':
net.cpp:29:13: 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:51:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for(i=0;i<C.size();i++)
~^~~~~~~~~
net.cpp:57:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for(j=0;j<v[ROOT].size();j++)
~^~~~~~~~~~~~~~~
net.cpp:69:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for(i=0;i<v[ROOT].size();i++)
~^~~~~~~~~~~~~~~
net.cpp:78:13: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
for(i=0;i<C.size();i++)
~^~~~~~~~~
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
6 ms |
5112 KB |
Output is correct |
| 2 |
Incorrect |
6 ms |
5112 KB |
Breaking single line is causing network to disconnect. |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
6 ms |
5112 KB |
Output is correct |
| 2 |
Incorrect |
6 ms |
5112 KB |
Breaking single line is causing network to disconnect. |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
6 ms |
5112 KB |
Output is correct |
| 2 |
Incorrect |
6 ms |
5112 KB |
Breaking single line is causing network to disconnect. |
| 3 |
Halted |
0 ms |
0 KB |
- |
