Submission #741209

#	Time	Username	Problem	Language	Result	Execution time	Memory
741209		n0sk1ll	Network (BOI15_net)	C++17	100 / 100	413 ms	57664 KiB

net

#include <bits/stdc++.h>

#define FAST ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);cerr.tie(0)
#define mp make_pair
#define xx first
#define yy second
#define pb push_back
#define pf push_front
#define popb pop_back
#define popf pop_front
#define all(x) x.begin(),x.end()
#define ff(i,a,b) for (int i = a; i < b; i++)
#define fff(i,a,b) for (int i = a; i <= b; i++)
#define bff(i,a,b) for (int i = b-1; i >= a; i--)
#define bfff(i,a,b) for (int i = b; i >= a; i--)

using namespace std;
long double typedef ld;
unsigned int typedef ui;
long long int typedef li;
pair<int,int> typedef pii;
pair<li,li> typedef pli;
pair<ld,ld> typedef pld;
vector<vector<int>> typedef graph;
unsigned long long int typedef ull;
//const int mod = 998244353;
const int mod = 1000000007;







//Note to self: Check for overflow

graph g(500005);

vector<int> listovi;
void dfs(int p, int q)
{
    if ((int)g[p].size()==1) listovi.pb(p);
    for (auto it : g[p]) if (it!=q) dfs(it,p);
}

int main()
{
    FAST;

    int n; cin>>n;
    ff(i,1,n)
    {
        int u,v; cin>>u>>v;
        g[u].pb(v),g[v].pb(u);
    }

    int root=-1;
    fff(i,1,n) if ((int)g[i].size()!=1) root=i;
    dfs(root,-1);

    vector<pii> ans;
    int m=(listovi).size();
    ff(i,0,(m+1)/2) ans.pb({listovi[i],listovi[(i+m/2)%m]});

    cout<<(int)ans.size()<<"\n";
    for (auto it : ans) cout<<it.xx<<" "<<it.yy<<"\n";
}

//Note to self: Check for overflow

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