Submission #959609

#	Time	Username	Problem	Language	Result	Execution time	Memory
959609		Blagoj	Network (BOI15_net)	C++17	100 / 100	376 ms	57968 KiB

net

#include <bits/stdc++.h>

using namespace std;

#define endl '\n'
#define ll long long
#define all(x) (x).begin(), (x).end()

const int mxn = 5e5 + 10;

vector<int> g[mxn], leafs;

void dfs(int cur, int par) {
    bool leaf = 1;
    for (auto x : g[cur]) {
        if (x == par) continue;
        leaf = 0;
        dfs(x, cur);
    }
    if (leaf) leafs.push_back(cur);
}

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int n;
    cin >> n;
    for (int i = 0; i < n - 1; i++) {
        int f, t;
        cin >> f >> t;
        g[f].push_back(t);
        g[t].push_back(f);
    }
    int root;
    for (int i = 1; i <= n; i++) if (g[i].size() >= 2) root = i;
    dfs(root, root);
    int sz = leafs.size();
    vector<pair<int, int>> v;
    for (int i = 0; i < sz / 2; i++) v.push_back({leafs[i], leafs[i + sz / 2]});
    if (sz % 2 != 0) v.push_back({leafs[0], leafs.back()});
    cout << v.size() << endl;
    for (auto x : v) cout << x.first << " " << x.second << endl;
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:36:8: warning: 'root' may be used uninitialized in this function [-Wmaybe-uninitialized]
   36 |     dfs(root, root);
      |     ~~~^~~~~~~~~~~~

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