Submission #987617

#	Time	Username	Problem	Language	Result	Execution time	Memory
987617		nihon	Network (BOI15_net)	C++14	0 / 100	4 ms	14940 KiB

net

#include <bits/stdc++.h>
#define N 500005
using namespace std;
int n,m,i,j,a,b,t,x,ok,l[N],f[N];
bool r[N];
vector<int> v[N];
vector<pair<int,int>> sol;
int main()
{
    cin>>n;
    for(i=1;i<n;++i)
    {
        cin>>a>>b;
        v[a].push_back(b);
        v[b].push_back(a);
    }
    for(i=2;i<=n;++i)
    {
        if(v[i].size()==1)
        {
            ++t;
            f[t]=i;
            l[i]=t;
        }
    }
    m=v[1].size();
    for(i=0;i<m;++i)
    {
        x=v[1][i];
        r[x]=1;
    }
    for(x=1;x<=n;++x)
    {
        if(r[x]) continue;
        if(l[x])
        {
            swap(f[t],f[l[x]]);
            ok=1;
            break;
        }
    }
    for(i=2;i<=t;i+=2)
    {
        sol.push_back({f[i-1],f[i]});
    }
    if(ok)
    {
        sol.push_back({1,f[t]});
    }
    m=sol.size();
    cout<<m<<'\n';
    for(i=0;i<m;++i)
    {
        cout<<sol[i].first<<' '<<sol[i].second<<'\n';
    }
    return 0;
}

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