Submission #629983

#	Time	Username	Problem	Language	Result	Execution time	Memory
629983		MinaRagy06	Network (BOI15_net)	C++17	0 / 100	1 ms	324 KiB

net

#include <bits/stdc++.h>
using namespace std;
#define lesgooo ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0)
#define endl    '\n'
#define int     long long

vector<vector<int>> adj;
int pos, mx = -1e18;
void dfs2(int i, int sum, int par)
{
    if (sum >= mx) mx = sum ,pos = i;
    for (auto nxt : adj[i]) if (nxt != par) dfs2(nxt, sum+1, i);
}
vector<pair<int, int>> dfs(int i, int par)
{
    if (adj[i].size() ==1) return {{0ll, i}};
    vector<pair<int, int>> ret;
    for (auto nxt : adj[i]) if (nxt != par)
    {
        vector<pair<int,int>> x = dfs(nxt ,i);
        for (auto &j : x) j.first++;
        ret.insert(ret.end(), x.begin(), x.end());
    }
    return ret;
}
signed main()
{
    lesgooo;
    int n, u, v;
    cin >> n;
    adj.resize(n);
    for (int i = 0; i < n-1; i++) cin >> u >> v, adj[--u].push_back(--v), adj[v].push_back(u);
    int idx = 0; mx = 0;
    for (int i = 0; i < n; i++) if ((int)adj[i].size() > mx) idx = i, mx = adj[i].size();
    vector<vector<pair<int,int>>> a;
    for (auto nxt : adj[idx]) a.push_back(dfs(nxt, idx));
    for (int i = 0; i < (int)a.size(); i++) sort(a[i].begin(), a[i].end());
    set<int> leaf;
    for (int i = 0; i < n; i++) if (adj[i].size() == 1) leaf.insert(i);
    vector<vector<int>> ans;
    while (1)
    {
        set<vector<int>> s;
        for (int i = 0; i < (int)a.size(); i++) if ((int)a[i].size()) s.insert({-a[i].back().first, a[i].back().second, i});
        if (s.empty()) break;
        if (s.size() == 1) break;
        vector<int> x = *s.begin(), y;
        s.erase(s.begin());
        y = *s.begin();
        a[x[2]].pop_back(), a[y[2]].pop_back();
        leaf.erase(x[1]), leaf.erase(y[1]);
        ans.push_back({x[1]+1, y[1]+1});
    }
    while (leaf.size() > 1)
    {
        int x = *leaf.begin(), y;
        leaf.erase(leaf.begin());
        y = *leaf.begin();
        leaf.erase(leaf.begin());
        ans.push_back({x+1, y+1});
    }
    if (leaf.size()) dfs2((*leaf.begin()), 0, -1), ans.push_back({(*leaf.begin())+1, pos+1});
    cout << ans.size() << endl;
    for (auto i : ans) cout << i[0] << " " << i[1] << endl;
    return 0;
}

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