# | 제출 시각 | 아이디 | 문제 | 언어 | 결과 | 실행 시간 | 메모리 |
---|---|---|---|---|---|---|---|
1263566 | dzhoz0 | Network (BOI15_net) | C++20 | 285 ms | 50456 KiB |
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define INF 1e18
#define f first
#define s second
#define pii pair<int, int>
#define vi vector<int>
const int MOD = 1'000'000'000 + 7;
void setIO(string name = "")
{
ios_base::sync_with_stdio(0);
cin.tie(0), cout.tie(0);
#ifdef LOCAL
freopen("inp.txt", "r", stdin);
freopen("out.txt", "w", stdout);
#else
if (!name.empty())
{
freopen((name + ".INP").c_str(), "r", stdin);
freopen((name + ".OUT").c_str(), "w", stdout);
}
#endif
}
const int MAXN = 5e5;
int n;
vi g[MAXN + 5];
vi leaves;
void dfs(int u, int par) {
int cnt = 0;
for(int v : g[u]) {
if(v == par) continue;
dfs(v, u);
cnt++;
}
if(cnt == 0 || g[u].size() == 1) leaves.push_back(u);
}
void solve()
{
cin >> n;
for(int i = 1; i < n; i++) {
int u, v; cin >> u >> v;
g[u].push_back(v);
g[v].push_back(u);
}
dfs(1, 1);
cout << ((int)leaves.size() + 1) / 2 << '\n';
for(int i = 0; i < (int)leaves.size() / 2; i++) {
cout << leaves[i] << ' ' << leaves[(int)leaves.size() / 2 + i] << '\n';
}
if((int)leaves.size() & 1) cout << leaves.back() << ' ' << leaves[0] << '\n';
}
signed main()
{
setIO();
int t = 1;
// cin >> t;
while (t--)
solve();
}
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