Submission #1189169

#	Time	Username	Problem	Language	Result	Execution time	Memory
1189169		njoop	Network (BOI15_net)	C++17	100 / 100	185 ms	45536 KiB

net

#include <bits/extc++.h>
using namespace std;
typedef long long ll;

vector<int> g[500010], leaves;

void dfs(int no, int pa) {
    if(g[no].size() == 1) {
        leaves.push_back(no);
    }
    for(auto i: g[no]) {
        if(i == pa) continue;
        dfs(i, no);
    }
}

int main(){
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    int n;
    cin>>n;
    for(int i=0;i<n-1;i++){
        int a,b;
        cin>>a>>b;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    dfs(1, 0);
    int l=leaves.size();
    int m=l/2;
    vector<pair<int,int>> ans;
    for(int i=0;i<m;i++){
        ans.emplace_back(leaves[i], leaves[i+m]);
    }
    if(l%2){
        ans.emplace_back(leaves[0], leaves[l-1]);
    }
    cout<<ans.size()<<"\n";
    for(auto &p: ans){
        cout<<p.first<<" "<<p.second<<"\n";
    }
    return 0;
}

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