#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
#define all(v) v.begin(), v.end()
#define pb push_back
#define ss second
#define ff first
#define vt vector
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
const int inf = 1e9;
const int mod = 1e9+7;
const int maxn = 5e5 + 1;
vt<pii> ans;
vt<int> g[maxn];
pii dfs(int v, int p){
int pr = -1, rp = -1;
if(g[v].size() == 1)pr = v;
for(auto i : g[v]){
if(i == p)continue;
pii wt = dfs(i, v);
if(pr == -1)pr = wt.ff;
else if(wt.ff != -1){
if(rp == -1)rp = wt.ff;
else {
ans.pb({rp, wt.ff});
rp = -1;
}
}
if(wt.ss != -1){
if(rp == -1)rp = wt.ss;
else {
ans.pb({rp, wt.ss});
rp = -1;
}
}
}
return {pr, rp};
}
void solve() {
int n;
cin >> n;
for(int i = 0, u, v; i < n - 1; i++){
cin >> u >> v;
g[u].pb(v), g[v].pb(u);
}
int t = 1;
for(int i = 1; i <= n; i++)if((int)g[i].size() > 1)t = i;
pii wt = dfs(t, 0);
if(wt.ss != -1)ans.pb({wt.ff, wt.ss});
else ans.pb({wt.ff, t});
cout << ans.size() << '\n';
for(auto i : ans)cout << i.ff << ' ' << i.ss << '\n';
}
int main() {
ios_base::sync_with_stdio(0);
cin.tie(0);
int times = 1;
//cin >> times;
for(int i = 1; i <= times; i++) {
solve();
}
return 0;
}
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
5 ms |
12376 KB |
Output is correct |
2 |
Correct |
4 ms |
12124 KB |
Output is correct |
3 |
Correct |
4 ms |
12124 KB |
Output is correct |
4 |
Correct |
4 ms |
12124 KB |
Output is correct |
5 |
Correct |
4 ms |
12124 KB |
Output is correct |
6 |
Correct |
4 ms |
12124 KB |
Output is correct |
7 |
Correct |
4 ms |
12124 KB |
Output is correct |
8 |
Correct |
4 ms |
12120 KB |
Output is correct |
9 |
Incorrect |
4 ms |
12124 KB |
Breaking single line is causing network to disconnect. |
10 |
Halted |
0 ms |
0 KB |
- |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
5 ms |
12376 KB |
Output is correct |
2 |
Correct |
4 ms |
12124 KB |
Output is correct |
3 |
Correct |
4 ms |
12124 KB |
Output is correct |
4 |
Correct |
4 ms |
12124 KB |
Output is correct |
5 |
Correct |
4 ms |
12124 KB |
Output is correct |
6 |
Correct |
4 ms |
12124 KB |
Output is correct |
7 |
Correct |
4 ms |
12124 KB |
Output is correct |
8 |
Correct |
4 ms |
12120 KB |
Output is correct |
9 |
Incorrect |
4 ms |
12124 KB |
Breaking single line is causing network to disconnect. |
10 |
Halted |
0 ms |
0 KB |
- |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
5 ms |
12376 KB |
Output is correct |
2 |
Correct |
4 ms |
12124 KB |
Output is correct |
3 |
Correct |
4 ms |
12124 KB |
Output is correct |
4 |
Correct |
4 ms |
12124 KB |
Output is correct |
5 |
Correct |
4 ms |
12124 KB |
Output is correct |
6 |
Correct |
4 ms |
12124 KB |
Output is correct |
7 |
Correct |
4 ms |
12124 KB |
Output is correct |
8 |
Correct |
4 ms |
12120 KB |
Output is correct |
9 |
Incorrect |
4 ms |
12124 KB |
Breaking single line is causing network to disconnect. |
10 |
Halted |
0 ms |
0 KB |
- |