#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using db = double;
using str = string; // yay python!
using pi = pair<int,int>;
using pl = pair<ll,ll>;
using pd = pair<db,db>;
using vi = vector<int>;
using vb = vector<bool>;
using vl = vector<ll>;
using vd = vector<db>;
using vs = vector<str>;
using vpi = vector<pi>;
using vpl = vector<pl>;
using vpd = vector<pd>;
// pairs
#define mp make_pair
#define f first
#define s second
// vectors
#define sz(x) (int)(x).size()
#define all(x) begin(x), end(x)
#define rall(x) (x).rbegin(), (x).rend()
#define sor(x) sort(all(x))
#define rsz resize
#define ins insert
#define ft front()
#define bk back()
#define pf push_front
#define pb push_back
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
// loops
#define FOR(i,a,b) for (int i = (a); i < (b); ++i)
#define F0R(i,a) FOR(i,0,a)
#define ROF(i,a,b) for (int i = (b)-1; i >= (a); --i)
#define R0F(i,a) ROF(i,0,a)
#define trav(a,x) for (auto& a: x)
const ll N = 5e5+5;
vector<int> adj[N];
int dist[N];
vl le;
int cnt = 0;
void dfs(int u,int p,int h){
dist[u] = h;
if(sz(adj[u]) == 1) {
cnt++;
le.pb(u);
}
for(auto v:adj[u]){
if(v!=p){
dfs(v,u,h+1);
}
}
}
bool cmp(int i,int j){
return dist[i] < dist[j];
}
int main() {
// you should actually read the stuff at the bottom
int n;
cin >> n;
for(int i =2;i<=n;i++){
int u,v;
cin>>u>>v;
adj[u].pb(v);
adj[v].pb(u);
}
dfs(1,0,0);
if(cnt%2==0){
cnt ++ ;
cnt /= 2;
cout << cnt << endl;
for(int i =0;i<cnt;i++){
cout << le[i] << " " << le[i+(sz(le))-i-1] << endl;
}
return 0;
}
cout << (cnt + 1) / 2 << endl;
cnt ++;
cnt /= 2;
for(int i =0;i<cnt-1;i++){
cout << le[i] << " " << le[(sz(le)) - i -1] << endl;
}
cout << le[0] << " " << le.back() << endl;
return 0;
}
/* stuff you should look for
* read the probem 3 more times in case of WA :)
* int overflow, array bounds
* special cases (n=1?)
* do smth instead of nothing and stay organized
* WRITE STUFF DOWN
* DON'T GET STUCK ON ONE APPROACH
*/
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
8 ms |
12032 KB |
Output is correct |
| 2 |
Incorrect |
8 ms |
12120 KB |
Breaking single line is causing network to disconnect. |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
8 ms |
12032 KB |
Output is correct |
| 2 |
Incorrect |
8 ms |
12120 KB |
Breaking single line is causing network to disconnect. |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
8 ms |
12032 KB |
Output is correct |
| 2 |
Incorrect |
8 ms |
12120 KB |
Breaking single line is causing network to disconnect. |
| 3 |
Halted |
0 ms |
0 KB |
- |
