Submission #1250827

#	Time	Username	Problem	Language	Result	Execution time	Memory
1250827		tradz	Network (BOI15_net)	C++20	0 / 100	2 ms	4168 KiB

net

#include <bits/stdc++.h>
#define TIME  (1.0 * clock() / CLOCKS_PER_SEC)
#define For(i,a,b) for(int i = a; i <= b; i++)
#define Ford(i,a,b) for(int i = a; i >= b; i--)
#define ll long long
#define ii pair<int,int>
#define fi first
#define se second
#define all(v) v.begin(),v.end()
#define RRH(v) v.resize(unique(all(v)) - v.begin())

using namespace std;
const int  N = 1e6+7;
const int M = 1e9+7;
const ll oo = 3e18;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
 
long long GetRandom(long long l, long long r) {
    return uniform_int_distribution<long long> (l, r)(rng);
}

int n; 
int cnt[N];

int main() {
    ios::sync_with_stdio(0); cin.tie(0);

    #define TASK ""
    if (fopen (".inp", "r")) {
        freopen (".inp", "r", stdin);
        freopen (".out", "w", stdout);
    }
    if(fopen(TASK".inp", "r")) {
        freopen(TASK".inp", "r", stdin);
        freopen(TASK".out", "w", stdout);
    }
    
    cin >> n;
    
    memset(cnt, 0, sizeof cnt);
    
    for (int i = 1; i < n; i++) {
        int u, v; cin >> u >> v;
        cnt[u]++;
        cnt[v]++;
    }
    
    vector <pair <int, int>> ans;
    vector <int> vertex;
    for (int i = 1; i <= n; i++) {
        if (cnt[i] == 1) vertex.push_back(i);
    }
    
    for (int i = 0; i < vertex.size(); i += 2) {
        int a = i;
        int b = (i + 1) % vertex.size();
        ans.push_back({vertex[a], vertex[b]});
    }
    
    cout << ans.size() << '\n';
    for (int i = 0; i < ans.size(); i++) cout << ans[i].first << " " << ans[i].second << '\n';

    cerr << "Time elapsed: " << TIME << " s.\n";
    return 0;
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:31:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   31 |         freopen (".inp", "r", stdin);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~
net.cpp:32:17: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   32 |         freopen (".out", "w", stdout);
      |         ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~
net.cpp:35:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   35 |         freopen(TASK".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:36:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   36 |         freopen(TASK".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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