Submission #1096977

#	Time	Username	Problem	Language	Result	Execution time	Memory
1096977		lmToT27	Network (BOI15_net)	C++17	100 / 100	291 ms	51920 KiB

net

#include <bits/stdc++.h>
#define all(dataStructure) dataStructure.begin(),dataStructure.end()
#define ll long long

using namespace std;
namespace std {
        template <typename T, int D>
        struct _vector : public vector <_vector <T, D - 1>> {
                static_assert(D >= 1, "Dimension must be positive!");
                template <typename... Args>
                _vector(int n = 0, Args... args) : vector <_vector <T, D - 1>> (n, _vector <T, D - 1> (args...)) {}
        };
        // _vector <int, 3> a(n, m, k);: int a[n][m][k].
        // _vector <int, 3> a(n, m, k, x);: int a[n][m][k] initialized with x.
        template <typename T>
        struct _vector <T, 1> : public vector <T> {
                _vector(int n = 0, const T& val = T()) : vector <T> (n, val) {}
        };
}

const int MAX = 5e5 + 3;
const ll MOD[] = {1000000007, 998244353};

int n;
vector <int> adj[MAX];
vector <int> f;

void dfs(int u, int pre) {
        for (int &v : adj[u]) {
                if (v != pre) dfs(v, u);
        }
        if (adj[u].size() == 1) f.push_back(u);
}

void Solve() {
        cin >> n;
        for (int i = 1; i < n; i++) {
                int u, v;
                cin >> u >> v;
                adj[u].push_back(v);
                adj[v].push_back(u);
        }
        dfs(1, 0);
        if (f.size() & 1) f.push_back(f[0]);
        cout << f.size() / 2 << '\n';
        int step = f.size() / 2;
        for (int i = 0; i < step; i++) {
                cout << f[i] << ' ' << f[i + step] << '\n';
        }
}

int32_t main() {
        ios_base::sync_with_stdio(0);
        cin.tie(0);

        #define TASK "TASK"
        if (fopen(TASK".INP", "r")) {
                freopen(TASK".INP", "r", stdin);
                freopen(TASK".OUT", "w", stdout);
        }
        
        /* int TEST = 1; cin >> TEST; while (TEST--) */ Solve();

        cerr << "\nTime elapsed: " << 1.0 * clock() / CLOCKS_PER_SEC << "s\n";
        return 0;
}

Compilation message (stderr)

net.cpp: In function 'int32_t main()':
net.cpp:58:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   58 |                 freopen(TASK".INP", "r", stdin);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:59:24: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   59 |                 freopen(TASK".OUT", "w", stdout);
      |                 ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

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