Submission #655830

#	Time	Username	Problem	Language	Result	Execution time	Memory
655830		as111	Network (BOI15_net)	C++14	100 / 100	573 ms	47704 KiB

net

//simple dfs
#include <vector>
#include <iostream>

#define MAXN 500000
#define pb push_back
#define fi first
#define se second
using namespace std;
vector<int> adj[MAXN + 5];
vector<int> leaf;
void dfs(int u, int par)
{
    if (adj[u].size() == 1) leaf.pb(u);
    for (int v : adj[u])
    {
        if (v == par) continue;
        dfs(v, u);
    }
}
void Solve()
{
    dfs(1, 0);
    int l = 0, step = (int)(leaf.size() / 2);
    if (leaf.size() % 2 == 0)
    {
        cout << leaf.size() / 2 << '\n';
        while (l + step < (int)leaf.size())
        {
            cout << leaf[l] << " " << leaf[l + step] << '\n';
            l++;
        }
        return;
    }
    leaf.pb(leaf[0]);
    step++;
    cout << leaf.size() / 2 << '\n';
    while (l + step < leaf.size())
    {
        cout << leaf[l] << " " << leaf[l + step] << '\n';
        l++;
    }
}
int main() {
    int N;
    cin >> N;
    for (int i = 1; i < N; i++)
    {
        int u, v;
        cin >> u >> v;
        adj[u].pb(v);
        adj[v].pb(u);
    }
    Solve();
}

Compilation message (stderr)

net.cpp: In function 'void Solve()':
net.cpp:38:21: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   38 |     while (l + step < leaf.size())
      |            ~~~~~~~~~^~~~~~~~~~~~~

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