Submission #1064044

#	Time	Username	Problem	Language	Result	Execution time	Memory
1064044		manhlinh1501	Network (BOI15_net)	C++17	100 / 100	251 ms	47824 KiB

net

#include <bits/stdc++.h>
using namespace std;
using i64 = long long;
const int MAXN = 5e5 + 5;
using pii = pair<int, int>;
int N;
vector<int> adj[MAXN];
vector<int> leaves;

void DFS(int u, int p) {
    if(adj[u].size() == 1) {
        leaves.emplace_back(u);
        return void(0);
    }
    for(int v : adj[u]) {
        if(v == p) continue;
        DFS(v, u);
    }
}

signed main() {
#define TASK "code"

    if (fopen(TASK ".inp", "r")) {
        freopen(TASK ".inp", "r", stdin);
        freopen(TASK ".out", "w", stdout);
    }

    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);

    cin >> N;
    for(int i = 1; i < N; i++) {
        int u, v;
        cin >> u >> v;
        adj[u].emplace_back(v);
        adj[v].emplace_back(u);
    }
    for(int i = 1; i <= N; i++) {
        if(adj[i].size() > 1) {
            DFS(i, 0);
            break;
        }
    }
    if(leaves.size() == 1) return cout << 0, 0;

    int k = leaves.size() / 2;

    cout << (leaves.size() + 1) / 2 << "\n";
    for(int i = 0; i < k; i++)
        cout << leaves[i] << " " << leaves[i + k] << "\n";
    if(leaves.size() % 2)
        cout << leaves.back() << " " << leaves[k] << "\n";

    return (0 ^ 0);
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:25:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   25 |         freopen(TASK ".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:26:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   26 |         freopen(TASK ".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~

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