#include<bits/stdc++.h>
#define int long long
#define pb push_back
#define fi first
#define se second
using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int maxN = 1e6 + 5;
const int mod = 1e9 + 7;
const ll oo = 1e18;
int n;
vector<int> adj[maxN];
int depth[maxN];
void ReadInput()
{
cin >> n;
for(int i=1; i<n; i++)
{
int u, v;
cin >> u >> v;
adj[u].pb(v);
adj[v].pb(u);
}
}
void dfs(int u, int par)
{
for(int v : adj[u])
{
if(v == par) continue;
depth[v] = depth[u] + 1;
dfs(v, u);
}
}
void Solve()
{
dfs(1, 0);
vector<int> leaf;
for(int i=1; i<=n; i++)
{
if(adj[i].size() == 1) leaf.pb(i);
}
sort(leaf.begin(), leaf.end(), [](int i, int j)
{
return depth[i] < depth[j];
});
if(leaf.size() % 2 == 0)
{
cout << leaf.size() / 2 << '\n';
int l = 0, r = leaf.size() - 1;
while(l < r)
{
cout << leaf[l] << " " << leaf[r] << '\n';
l++;
r--;
}
return;
}
cout << leaf.size() / 2 + 1 << '\n';
int l = 0, r = leaf.size() - 1;
while(l < r)
{
cout << leaf[l] << " " << leaf[r] << '\n';
l++;
r--;
}
for(int i=1; i<=n; i++)
{
if(i != adj[leaf.back()][0])
{
cout << leaf.back() << " " << i;
return;
}
}
}
int32_t main()
{
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
ReadInput();
Solve();
}
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
14 ms |
23764 KB |
Output is correct |
2 |
Correct |
12 ms |
23740 KB |
Output is correct |
3 |
Correct |
13 ms |
23764 KB |
Output is correct |
4 |
Incorrect |
13 ms |
23768 KB |
Breaking single line is causing network to disconnect. |
5 |
Halted |
0 ms |
0 KB |
- |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
14 ms |
23764 KB |
Output is correct |
2 |
Correct |
12 ms |
23740 KB |
Output is correct |
3 |
Correct |
13 ms |
23764 KB |
Output is correct |
4 |
Incorrect |
13 ms |
23768 KB |
Breaking single line is causing network to disconnect. |
5 |
Halted |
0 ms |
0 KB |
- |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
14 ms |
23764 KB |
Output is correct |
2 |
Correct |
12 ms |
23740 KB |
Output is correct |
3 |
Correct |
13 ms |
23764 KB |
Output is correct |
4 |
Incorrect |
13 ms |
23768 KB |
Breaking single line is causing network to disconnect. |
5 |
Halted |
0 ms |
0 KB |
- |