#include "bits/extc++.h"
using namespace std;
template <typename T, typename... U>
void dbgh(const T& t, const U&... u) {
cerr << t;
((cerr << " | " << u), ...);
cerr << endl;
}
#ifdef DEBUG
#define dbg(...) \
cerr << "L" << __LINE__ << " [" << #__VA_ARGS__ << "]" \
<< ": "; \
dbgh(__VA_ARGS__)
#else
#define cerr \
if (false) \
cerr
#define dbg(...)
#endif
#define endl "\n"
#define long int64_t
#define sz(x) int(std::size(x))
constexpr int maxn = 5e5 + 5;
int r1[maxn];
vector<pair<int, int>> ans;
vector<int> graph[maxn];
void pdfs(int u, int p, int r) {
if (r == -1 && p != -1) {
r = u;
}
r1[u] = r;
for (auto& v : graph[u]) {
if (v == p) {
continue;
}
pdfs(v, u, r);
}
}
vector<int> dfs(int u, int p) {
if (sz(graph[u]) == 1) {
return {u};
}
vector<int> unmatched;
for (auto& v : graph[u]) {
if (v == p) {
continue;
}
auto ch = dfs(v, u);
while (sz(unmatched) > 1 && sz(ch)) {
ans.emplace_back(unmatched.back(), ch.back());
unmatched.pop_back();
ch.pop_back();
}
unmatched.insert(unmatched.end(), begin(ch), end(ch));
assert(sz(unmatched) <= 3);
}
if (sz(unmatched) == 3) {
ans.emplace_back(unmatched[0], unmatched[1]);
unmatched = {unmatched[2]};
}
if (p == -1 && sz(unmatched)) {
if (sz(unmatched) == 2) {
ans.emplace_back(unmatched[0], unmatched[1]);
} else {
assert(sz(unmatched) == 1);
int left = unmatched[0];
for (auto& v : graph[u]) {
assert(v == r1[v]);
if (v != r1[left]) {
ans.emplace_back(v, left);
unmatched.pop_back();
break;
}
}
assert(!sz(unmatched));
}
}
return unmatched;
}
void solve() {
int n;
cin >> n;
for (int i = 0; i < n - 1; i++) {
int u, v;
cin >> u >> v;
u--;
v--;
graph[u].push_back(v);
graph[v].push_back(u);
}
for (int i = 0; i < n; i++) {
if (sz(graph[i]) < 2) {
continue;
}
pdfs(i, -1, -1);
dfs(i, -1);
break;
}
cout << sz(ans) << endl;
for (auto& [u, v] : ans) {
cout << u + 1 << " " << v + 1 << endl;
}
}
int main() {
cin.tie(nullptr);
cin.exceptions(ios::failbit);
ios_base::sync_with_stdio(false);
solve();
}
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
6 ms |
12076 KB |
Output is correct |
2 |
Correct |
7 ms |
12076 KB |
Output is correct |
3 |
Correct |
6 ms |
11988 KB |
Output is correct |
4 |
Correct |
6 ms |
12012 KB |
Output is correct |
5 |
Correct |
5 ms |
12068 KB |
Output is correct |
6 |
Correct |
6 ms |
11988 KB |
Output is correct |
7 |
Correct |
6 ms |
12072 KB |
Output is correct |
8 |
Correct |
6 ms |
11964 KB |
Output is correct |
9 |
Correct |
6 ms |
11988 KB |
Output is correct |
10 |
Correct |
5 ms |
11988 KB |
Output is correct |
11 |
Correct |
7 ms |
12068 KB |
Output is correct |
12 |
Correct |
6 ms |
11988 KB |
Output is correct |
13 |
Correct |
6 ms |
11976 KB |
Output is correct |
14 |
Correct |
6 ms |
12068 KB |
Output is correct |
15 |
Correct |
6 ms |
11988 KB |
Output is correct |
16 |
Correct |
6 ms |
11988 KB |
Output is correct |
17 |
Correct |
6 ms |
12076 KB |
Output is correct |
18 |
Correct |
5 ms |
12036 KB |
Output is correct |
19 |
Correct |
6 ms |
11988 KB |
Output is correct |
20 |
Correct |
5 ms |
11988 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
6 ms |
12076 KB |
Output is correct |
2 |
Correct |
7 ms |
12076 KB |
Output is correct |
3 |
Correct |
6 ms |
11988 KB |
Output is correct |
4 |
Correct |
6 ms |
12012 KB |
Output is correct |
5 |
Correct |
5 ms |
12068 KB |
Output is correct |
6 |
Correct |
6 ms |
11988 KB |
Output is correct |
7 |
Correct |
6 ms |
12072 KB |
Output is correct |
8 |
Correct |
6 ms |
11964 KB |
Output is correct |
9 |
Correct |
6 ms |
11988 KB |
Output is correct |
10 |
Correct |
5 ms |
11988 KB |
Output is correct |
11 |
Correct |
7 ms |
12068 KB |
Output is correct |
12 |
Correct |
6 ms |
11988 KB |
Output is correct |
13 |
Correct |
6 ms |
11976 KB |
Output is correct |
14 |
Correct |
6 ms |
12068 KB |
Output is correct |
15 |
Correct |
6 ms |
11988 KB |
Output is correct |
16 |
Correct |
6 ms |
11988 KB |
Output is correct |
17 |
Correct |
6 ms |
12076 KB |
Output is correct |
18 |
Correct |
5 ms |
12036 KB |
Output is correct |
19 |
Correct |
6 ms |
11988 KB |
Output is correct |
20 |
Correct |
5 ms |
11988 KB |
Output is correct |
21 |
Correct |
6 ms |
12076 KB |
Output is correct |
22 |
Correct |
6 ms |
12116 KB |
Output is correct |
23 |
Correct |
8 ms |
12244 KB |
Output is correct |
24 |
Correct |
6 ms |
12120 KB |
Output is correct |
25 |
Correct |
6 ms |
12116 KB |
Output is correct |
26 |
Correct |
7 ms |
12116 KB |
Output is correct |
27 |
Correct |
6 ms |
12084 KB |
Output is correct |
28 |
Correct |
6 ms |
12116 KB |
Output is correct |
29 |
Correct |
6 ms |
12056 KB |
Output is correct |
30 |
Correct |
5 ms |
12016 KB |
Output is correct |
31 |
Correct |
6 ms |
12080 KB |
Output is correct |
32 |
Correct |
6 ms |
12072 KB |
Output is correct |
33 |
Correct |
6 ms |
11988 KB |
Output is correct |
34 |
Correct |
6 ms |
11988 KB |
Output is correct |
35 |
Correct |
6 ms |
11988 KB |
Output is correct |
36 |
Correct |
7 ms |
12076 KB |
Output is correct |
37 |
Correct |
5 ms |
12116 KB |
Output is correct |
38 |
Correct |
7 ms |
12208 KB |
Output is correct |
39 |
Correct |
7 ms |
12072 KB |
Output is correct |
40 |
Correct |
5 ms |
11988 KB |
Output is correct |
41 |
Correct |
6 ms |
12068 KB |
Output is correct |
42 |
Correct |
6 ms |
11988 KB |
Output is correct |
43 |
Correct |
6 ms |
12076 KB |
Output is correct |
44 |
Correct |
6 ms |
11988 KB |
Output is correct |
45 |
Correct |
7 ms |
11988 KB |
Output is correct |
46 |
Correct |
6 ms |
12072 KB |
Output is correct |
47 |
Correct |
7 ms |
12072 KB |
Output is correct |
48 |
Correct |
6 ms |
11988 KB |
Output is correct |
49 |
Correct |
6 ms |
12108 KB |
Output is correct |
50 |
Correct |
6 ms |
12028 KB |
Output is correct |
51 |
Correct |
6 ms |
12068 KB |
Output is correct |
52 |
Correct |
6 ms |
12116 KB |
Output is correct |
53 |
Correct |
6 ms |
12116 KB |
Output is correct |
54 |
Correct |
7 ms |
12032 KB |
Output is correct |
55 |
Correct |
6 ms |
11988 KB |
Output is correct |
56 |
Correct |
6 ms |
11988 KB |
Output is correct |
57 |
Correct |
7 ms |
12068 KB |
Output is correct |
58 |
Correct |
6 ms |
12116 KB |
Output is correct |
# |
결과 |
실행 시간 |
메모리 |
Grader output |
1 |
Correct |
6 ms |
12076 KB |
Output is correct |
2 |
Correct |
7 ms |
12076 KB |
Output is correct |
3 |
Correct |
6 ms |
11988 KB |
Output is correct |
4 |
Correct |
6 ms |
12012 KB |
Output is correct |
5 |
Correct |
5 ms |
12068 KB |
Output is correct |
6 |
Correct |
6 ms |
11988 KB |
Output is correct |
7 |
Correct |
6 ms |
12072 KB |
Output is correct |
8 |
Correct |
6 ms |
11964 KB |
Output is correct |
9 |
Correct |
6 ms |
11988 KB |
Output is correct |
10 |
Correct |
5 ms |
11988 KB |
Output is correct |
11 |
Correct |
7 ms |
12068 KB |
Output is correct |
12 |
Correct |
6 ms |
11988 KB |
Output is correct |
13 |
Correct |
6 ms |
11976 KB |
Output is correct |
14 |
Correct |
6 ms |
12068 KB |
Output is correct |
15 |
Correct |
6 ms |
11988 KB |
Output is correct |
16 |
Correct |
6 ms |
11988 KB |
Output is correct |
17 |
Correct |
6 ms |
12076 KB |
Output is correct |
18 |
Correct |
5 ms |
12036 KB |
Output is correct |
19 |
Correct |
6 ms |
11988 KB |
Output is correct |
20 |
Correct |
5 ms |
11988 KB |
Output is correct |
21 |
Correct |
6 ms |
12076 KB |
Output is correct |
22 |
Correct |
6 ms |
12116 KB |
Output is correct |
23 |
Correct |
8 ms |
12244 KB |
Output is correct |
24 |
Correct |
6 ms |
12120 KB |
Output is correct |
25 |
Correct |
6 ms |
12116 KB |
Output is correct |
26 |
Correct |
7 ms |
12116 KB |
Output is correct |
27 |
Correct |
6 ms |
12084 KB |
Output is correct |
28 |
Correct |
6 ms |
12116 KB |
Output is correct |
29 |
Correct |
6 ms |
12056 KB |
Output is correct |
30 |
Correct |
5 ms |
12016 KB |
Output is correct |
31 |
Correct |
6 ms |
12080 KB |
Output is correct |
32 |
Correct |
6 ms |
12072 KB |
Output is correct |
33 |
Correct |
6 ms |
11988 KB |
Output is correct |
34 |
Correct |
6 ms |
11988 KB |
Output is correct |
35 |
Correct |
6 ms |
11988 KB |
Output is correct |
36 |
Correct |
7 ms |
12076 KB |
Output is correct |
37 |
Correct |
5 ms |
12116 KB |
Output is correct |
38 |
Correct |
7 ms |
12208 KB |
Output is correct |
39 |
Correct |
7 ms |
12072 KB |
Output is correct |
40 |
Correct |
5 ms |
11988 KB |
Output is correct |
41 |
Correct |
6 ms |
12068 KB |
Output is correct |
42 |
Correct |
6 ms |
11988 KB |
Output is correct |
43 |
Correct |
6 ms |
12076 KB |
Output is correct |
44 |
Correct |
6 ms |
11988 KB |
Output is correct |
45 |
Correct |
7 ms |
11988 KB |
Output is correct |
46 |
Correct |
6 ms |
12072 KB |
Output is correct |
47 |
Correct |
7 ms |
12072 KB |
Output is correct |
48 |
Correct |
6 ms |
11988 KB |
Output is correct |
49 |
Correct |
6 ms |
12108 KB |
Output is correct |
50 |
Correct |
6 ms |
12028 KB |
Output is correct |
51 |
Correct |
6 ms |
12068 KB |
Output is correct |
52 |
Correct |
6 ms |
12116 KB |
Output is correct |
53 |
Correct |
6 ms |
12116 KB |
Output is correct |
54 |
Correct |
7 ms |
12032 KB |
Output is correct |
55 |
Correct |
6 ms |
11988 KB |
Output is correct |
56 |
Correct |
6 ms |
11988 KB |
Output is correct |
57 |
Correct |
7 ms |
12068 KB |
Output is correct |
58 |
Correct |
6 ms |
12116 KB |
Output is correct |
59 |
Correct |
303 ms |
37796 KB |
Output is correct |
60 |
Correct |
334 ms |
40696 KB |
Output is correct |
61 |
Correct |
6 ms |
12040 KB |
Output is correct |
62 |
Correct |
5 ms |
11988 KB |
Output is correct |
63 |
Correct |
203 ms |
35064 KB |
Output is correct |
64 |
Correct |
8 ms |
13396 KB |
Output is correct |
65 |
Correct |
15 ms |
17364 KB |
Output is correct |
66 |
Correct |
126 ms |
60528 KB |
Output is correct |
67 |
Correct |
545 ms |
99220 KB |
Output is correct |
68 |
Correct |
592 ms |
101204 KB |
Output is correct |
69 |
Correct |
11 ms |
12980 KB |
Output is correct |
70 |
Correct |
79 ms |
21812 KB |
Output is correct |
71 |
Correct |
252 ms |
43848 KB |
Output is correct |
72 |
Correct |
279 ms |
42664 KB |
Output is correct |
73 |
Correct |
69 ms |
19548 KB |
Output is correct |
74 |
Correct |
456 ms |
39624 KB |
Output is correct |
75 |
Correct |
24 ms |
15460 KB |
Output is correct |
76 |
Correct |
272 ms |
43652 KB |
Output is correct |
77 |
Correct |
258 ms |
43548 KB |
Output is correct |
78 |
Correct |
33 ms |
19564 KB |
Output is correct |
79 |
Correct |
576 ms |
90560 KB |
Output is correct |
80 |
Correct |
8 ms |
12244 KB |
Output is correct |
81 |
Correct |
67 ms |
21964 KB |
Output is correct |
82 |
Correct |
343 ms |
41428 KB |
Output is correct |
83 |
Correct |
392 ms |
39596 KB |
Output is correct |
84 |
Correct |
342 ms |
39560 KB |
Output is correct |
85 |
Correct |
352 ms |
39616 KB |
Output is correct |
86 |
Correct |
341 ms |
40708 KB |
Output is correct |
87 |
Correct |
333 ms |
40692 KB |
Output is correct |