Submission #1189030

#	Time	Username	Problem	Language	Result	Execution time	Memory
1189030		rendel	Network (BOI15_net)	C++20	0 / 100	7 ms	12104 KiB

net

#include<bits/stdc++.h>
using namespace std;
const int maxn = 5e5+5;
int deg[maxn];
vector<int> adj[maxn];

bool chk(int i,int j){
    for(auto a : adj[i]){
        for(auto b : adj[j]){
            if(a==b) return false;
        }
    }
    return true;
}
int main(){
    cin.tie(nullptr)->sync_with_stdio(false); cout.tie(0);

    int n; cin >> n;
    for(int i=0;i<n-1;++i){
        int a,b; cin >> a >> b;
        adj[a].emplace_back(b);
        adj[b].emplace_back(a);
        deg[a]++, deg[b]++;
    }

    vector<int> g;
    for(int i=1;i<=n;++i){
        if(deg[i]==1) g.emplace_back(i);
    }

    int l=g.size();
    cout << (l+1)/2 << '\n';
    vector<bool> vis(l,false);
    vector<int> vec;
    for(int i=1;i<l;++i){
        if(chk(g[i],g[i-1]) && !vis[i] && !vis[i-1]){
            cout << g[i] << ' ' << g[i-1] << '\n';
            vis[i]=1; vis[i-1]=1;
        }
        if(!vis[i] && i==l-1) vec.emplace_back(i);
        if(!vis[i-1]) vec.emplace_back(i-1);
    }
    //for(auto i : vec) cout << i << ' ';
    if(vec.size()>1){
        for(int i=1;i<vec.size();++i){
            if(!vis[vec[i]] && !vis[vec[i-1]]){
                cout << g[vec[i]] << ' ' << g[vec[i-1]] << '\n';
                vis[vec[i]]=1; vis[vec[i-1]]=1;
            }
        }
    }
    for(int i=1;i<l;++i){
        if(!vis[i]){
            cout << g[i] << ' ' << g[i-1] << '\n';
        }
    }
}

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