Submission #1213424

#	Time	Username	Problem	Language	Result	Execution time	Memory
1213424		minhpk	Network (BOI15_net)	C++20	0 / 100	10 ms	23932 KiB

net

#include <bits/stdc++.h>
#define int long long
using namespace std;
int a;
mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
vector<int> z[1000005];
vector <int> v;
int sta[1000005];
int fin[1000005];
int tour;
bool cmp(int a,int b){
    return sta[a]<sta[b];
}
bool check[100005];
int par[1000005];
void dfs(int i,int parent){
    par[i]=parent;
    sta[i]=tour;
    tour++;
    for (auto p:z[i]){
         if (p==parent){
             continue;
         }
         dfs(p,i);
    }
    fin[i]=tour;
}
signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cin >> a;
    for (int i=1;i<a;i++){
         int x,y;
         cin >> x >> y;
         z[y].push_back(x);
         z[x].push_back(y);
    }
    for (int i=1;i<=a;i++){
         if (z[i].size()==1){
            // cout << "ok" << "\n";
             check[i]=true;
             v.push_back(i);
         }
    }
    dfs(1,0);

    int k=v.size();
    cout << (k+1)/2 << "\n";

    if (k%2==1){
        int x=v[k-1];
        for (int i=1;i<=a;i++){
             if (!check[i] && par[x]!=i){
                 cout << x << ' ' << i << "\n";
                 v.pop_back();
             }
        }
    }
    sort(v.begin(),v.end(),cmp);
    int l=0;
    int r=v.size()-1;
    while (l<=r){
         cout << v[l] << " " << v[r] << "\n";
         l++;
         r--;
    }
    return 0;
}

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