Submission #1270606

#	Time	Username	Problem	Language	Result	Execution time	Memory
1270606		bjp123	Network (BOI15_net)	C++20	100 / 100	194 ms	50596 KiB

net

#include <bits/stdc++.h>
#define ll long long
#define fi first
#define se second
#define pb push_back
#define ii pair<ll, ll>
#define all(a) a.begin(), a.end()
#define iii pair<ll,ii>
using namespace std;


const ll N =1e6+5;
const ll mod = 998244353;
const ll inf=1e18;

ll n,i,j,m,q,k,t,x,y;

vector<ll> v[N],ans;
ll timedfs=0;
void dfs(ll u,ll p)
{
    ++timedfs;
    if(v[u].size()==1) ans.pb(u);
    for(auto x:v[u])
        if(x!=p) dfs(x,u);
}
int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
cin>>n;
for(i=1;i<n;i++)
{
    cin>>x>>y;
    v[x].pb(y);
    v[y].pb(x);
}
for(i=1;i<=n;i++)
    if(v[i].size()>1)
{
    dfs(i,0);
    // solve
    ll sz=ans.size();
    cout<<(sz+1)/2<<'\n';
    for(i=0;i+(sz+1)/2<sz;i++)
        cout<<ans[i]<<" "<<ans[i+(sz+1)/2]<<'\n';
    if(sz&1) cout<<ans[sz/2]<<" "<<i<<'\n';
    return 0;
}
return 0;
}
/*

*/

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