Submission #1189049

#	Time	Username	Problem	Language	Result	Execution time	Memory
1189049		pxsit	Network (BOI15_net)	C++20	18 / 100	284 ms	14244 KiB

net

#include <bits/stdc++.h>
using namespace std;
int n,m,k,q;
vector<int> adj[(int)5e5+5];
vector<int> dep((int)5e5+5);
vector<pair<int,int>> vs;
void dfs(int x, int i){
    if(adj[x].size() == 1){
        vs.emplace_back(dep[x], x);
        return;
    }
    for(auto to:adj[x]){
        if(to == i) continue;
        dep[to] = dep[x] + 1;
        dfs(to, x);
    }
}
int main(){
    cin >> n;
    for(int i = 2; i <= n; i++){
        int a,b;
        cin >> a >> b;
        adj[a].push_back(b);
        adj[b].push_back(a);
    }
    vector<pair<int,int>> u;
    int sz = INT_MAX;
    for(int i = 1; i <= n; i++){
        vector<pair<int,int>> ans;
        vector<int> op;
        for(auto to : adj[i]){
            dep[to] = 1;
            vs.clear();
            dfs(to, i);
            sort(vs.begin(), vs.end(), greater<pair<int,int>>());
            ans.emplace_back(i, vs[0].second);
            for(int j = 2; j < vs.size(); j += 2){
                ans.emplace_back(vs[j-1].second, vs[j].second);
            }
            if(vs.size() % 2 == 0){
                op.push_back(vs.back().second);
            }
        }
        for(int k = 1; k < op.size(); k += 2){
            ans.emplace_back(op[k-1], op[k]);
        }
        if(op.size() % 2 == 1){
            ans.emplace_back(op.back(), i);
        }
        if(sz > ans.size()){
            u = ans;
            sz = ans.size();
        }
    }
    cout << u.size() << "\n";
    for(auto [a, b] : u){
        cout << a << " " << b << "\n";
    }
}

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