Submission #1189067

#	Time	Username	Problem	Language	Result	Execution time	Memory
1189067		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],h[maxn];
vector<int> adj[maxn];

void dfs(int u,int p){
    for(auto v : adj[u]){
        if(v==p) continue;
        h[v]=h[u]+1;
        dfs(v,u);
    }
}

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]++;
    }
    dfs(1,0);

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

    int l=g.size();
    cout << (l+1)/2 << '\n';
    sort(g.begin(),g.end());
    for(int i=0;i<l/2;++i){
        cout << g[i].second << ' ' << g[l-i-1].second <<'\n'; 
    }
    if(l%2==1) cout << g[l-1].second << ' ' << g[l/2].second ;
}

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