Submission #1064020

#	Time	Username	Problem	Language	Result	Execution time	Memory
1064020		manhlinh1501	Network (BOI15_net)	C++17	0 / 100	6 ms	12124 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;

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)
            leaves.emplace_back(i);
    }

    if(leaves.size() == 1) return cout << 0, 0;
    if(leaves.size() == 2 or leaves.size() == 3) {
        cout << leaves.size() - 1 << "\n";
        for(int i = 0; i < leaves.size() - 1; i++)
            cout << leaves[i] << " " << leaves[i + 1] << "\n";
        return 0;
    }
    vector<pii> ans;
    for(int i = 0; i < leaves.size() / 2; i++)
        ans.emplace_back(leaves[i], leaves[leaves.size() - i - 1]);
    if(leaves.size() % 2 == 1) ans.emplace_back(leaves[leaves.size() / 2], leaves.front());
    cout << ans.size() << "\n";
    for(auto [x, y] : ans)
        cout << x << " " << y << "\n";
    return (0 ^ 0);
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:38:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   38 |         for(int i = 0; i < leaves.size() - 1; i++)
      |                        ~~^~~~~~~~~~~~~~~~~~~
net.cpp:43:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   43 |     for(int i = 0; i < leaves.size() / 2; i++)
      |                    ~~^~~~~~~~~~~~~~~~~~~
net.cpp:14:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   14 |         freopen(TASK ".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:15:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   15 |         freopen(TASK ".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~

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