// Possible Overdose for this coder
#include <bits/stdc++.h>
#define put(x) cerr << #x << ": " << x << '\n'
#define line() cerr << "**************\n"
//#define F first
//#define S second
//#define mul(x, y) (((x) * (y)) %mod)
//#define bit(i, j) (((i)>>(j)) &1)
//#define left(id) ((id<<1) + 1)
//#define right(id) ((id<<1) + 2)
using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<pii, int> piii;
const int maxn = 5e5 + 10;
int n;
vector <int> G[maxn];
bool mark[maxn];
int leaves[maxn], num;
void dfs(int v){
mark[v] = 1;
if(G[v].size() == 1)
leaves[v] = 1;
for(int u: G[v]){
if(mark[u])
continue;
dfs(u);
leaves[v] += leaves[u];
}
}
vector <int> s[maxn];
void make(int v, int x){
mark[v] = 1;
if(G[v].size() == 1)
s[x].push_back(v);
for(int u: G[v]){
if(mark[u])
continue;
make(u, x);
}
}
int find(int v){
mark[v] = 1;
for(int u: G[v]){
if(mark[u])
continue;
if(leaves[u] > num /2)
return find(u);
}
return v;
}
int cnt = 0;
void solve(int root){
dfs(root);
num = leaves[root];
fill(mark, mark+maxn, 0);
int V = find(root);
fill(mark, mark+maxn, 0);
mark[V] = 1;
for(int u: G[V])
make(u, cnt++);
}
int main(){
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
cin >> n;
if(n == 1)
return cout << "0\n", 0;
if(n == 2)
return cout << "1\n1 2\n", 0;
int u, v;
for(int i=1; i<n; i++){
cin >> u >> v;
G[u].push_back(v), G[v].push_back(u);
}
int root = 1;
for(int v=1; v<=n; v++)
if(G[v].size() > 1)
root = v;
solve(root);
int res = (num+1) / 2;
vector <int> ans(2 * res);
int pt = 0;
for(int i=0; i<cnt; i++)
for(int vi: s[i]){
ans[pt] = vi;
pt += 2;
if(pt == 2 * res)
pt = 1;
}
if((!ans.empty()) && ans.back() == 0)
ans.back() = s[1][0];
cout << res << '\n';
for(int i=0; i<(int)ans.size(); i+=2)
cout << ans[i] << ' ' << ans[i+1] << '\n';
}
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
16 ms |
24268 KB |
Output is correct |
| 2 |
Correct |
15 ms |
24260 KB |
Output is correct |
| 3 |
Correct |
15 ms |
24296 KB |
Output is correct |
| 4 |
Incorrect |
15 ms |
24268 KB |
Breaking single line is causing network to disconnect. |
| 5 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
16 ms |
24268 KB |
Output is correct |
| 2 |
Correct |
15 ms |
24260 KB |
Output is correct |
| 3 |
Correct |
15 ms |
24296 KB |
Output is correct |
| 4 |
Incorrect |
15 ms |
24268 KB |
Breaking single line is causing network to disconnect. |
| 5 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
16 ms |
24268 KB |
Output is correct |
| 2 |
Correct |
15 ms |
24260 KB |
Output is correct |
| 3 |
Correct |
15 ms |
24296 KB |
Output is correct |
| 4 |
Incorrect |
15 ms |
24268 KB |
Breaking single line is causing network to disconnect. |
| 5 |
Halted |
0 ms |
0 KB |
- |
