| # |
Submission time |
Handle |
Problem |
Language |
Result |
Execution time |
Memory |
| 902711 |
2024-01-11T01:12:13 Z |
aqxa |
Network (BOI15_net) |
C++17 |
|
1 ms |
456 KB |
#include <bits/stdc++.h>
using namespace std;
#define ll long long
// works?
struct graph {
vector<vector<int>> adj;
int n;
graph() {}
graph(int _n) : n(_n) {
adj.resize(n);
}
inline void add(int x, int y) {
adj[x].push_back(y);
adj[y].push_back(x);
}
};
struct lca_graph : graph {
using graph::adj;
using graph::n;
vector<vector<int>> par;
vector<int> lev, path;
int lv = 0, lg;
lca_graph(int _n) : graph(_n) {
lg = __lg(n) + 1;
par = vector<vector<int>>(n, vector<int>(lg, -1));
lev = vector<int>(n, 0);
}
void make_lca(int x, int p) {
path.push_back(x);
lv++;
lev[x] = lv;
for (int i = 0; (1<<i) < path.size(); ++i) {
par[x][i] = path[path.size()-1-(1<<i)];
}
for (auto u: adj[x]) {
if (u != p) {
make_lca(u, x);
}
}
lv--;
path.pop_back();
}
int ka(int u, int k) {
if (k > lev[u] - 1) return 0;
while (k > 0) {
int clg = (int) __lg(k);
k -= (1 << lg);
u = par[u][clg];
}
return u;
}
int lca(int u, int v) {
int du = lev[u], dv = lev[v];
if (du < dv) {
v = ka(v, dv - du);
dv = du;
} else if (du > dv) {
u = ka(u, du - dv);
du = dv;
}
if (u == v) return u;
for (int i = lg-1; i >= 0; --i) {
if (par[u][i] != par[v][i]) {
u = par[u][i];
v = par[v][i];
}
}
return par[u][0];
}
};
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0);
int n;
cin >> n;
lca_graph g(n);
for (int i = 0; i < n - 1; ++i) {
int x, y;
cin >> x >> y;
g.add(--x, --y);
}
vector<int> leafs;
set<int> leaf;
for (int i = 0; i < n; ++i) {
if ((int) g.adj[i].size() == 1) {
leaf.insert(i);
leafs.push_back(i);
}
}
for (int i = 0; i < n; ++i) {
if (leaf.find(i) == leaf.end()) {
g.make_lca(i, -1);
break;
}
}
vector<pair<int, int>> ans;
for (int i = 0; i + 1 < (int) leafs.size(); i += 2) {
if (!ans.size()) {
ans.push_back(make_pair(leafs[i], leafs[i + 1]));
continue;
}
auto p = ans.back();
ans.pop_back();
vector<int> v = {p.first, p.second, leafs[i], leafs[i + 1]};
int best = 0;
pair<int, int> c = {2 * n, 2 * n};
for (int f = 1; f < 4; ++f) {
int a = g.lca(v[0], v[f]), b;
for (int j = 1; j < 4; ++j) {
for (int k = j + 1; k < 4; ++k) {
if (j != f && k != f) {
b = g.lca(v[j], v[k]);
// cout << "Good\n";
}
}
}
a = g.lev[a];
b = g.lev[b];
if (a > b) swap(a, b);
pair<int, int> cur = {a, b};
if (cur < c) {
best = f;
c = cur;
}
}
// cout << "G\n";
// cout << best << '\n';
ans.push_back({v[0], v[best]});
for (int j = 1; j < 4; ++j) {
for (int k = j + 1; k < 4; ++k) {
if (j != best && k != best) {
ans.push_back({v[j], v[k]});
}
}
}
}
if ((int) leafs.size() % 2) {
int x = leafs.back();
for (int i = 0; i < n; ++i) {
if (i != x && i != g.adj[x][0]) {
ans.push_back({x, i});
break;
}
}
}
cout << (int) ans.size() << "\n";
for (auto [x, y]: ans) {
cout << x + 1 << " " << y + 1 << "\n";
}
return 0;
}
Compilation message
net.cpp: In member function 'void lca_graph::make_lca(int, int)':
net.cpp:37:32: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
37 | for (int i = 0; (1<<i) < path.size(); ++i) {
| ~~~~~~~^~~~~~~~~~~~~
net.cpp: In function 'int main()':
net.cpp:131:15: warning: 'b' may be used uninitialized in this function [-Wmaybe-uninitialized]
131 | b = g.lev[b];
| ^
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
348 KB |
Output is correct |
| 2 |
Correct |
1 ms |
348 KB |
Output is correct |
| 3 |
Correct |
0 ms |
348 KB |
Output is correct |
| 4 |
Correct |
1 ms |
348 KB |
Output is correct |
| 5 |
Correct |
1 ms |
348 KB |
Output is correct |
| 6 |
Correct |
1 ms |
348 KB |
Output is correct |
| 7 |
Correct |
0 ms |
348 KB |
Output is correct |
| 8 |
Correct |
0 ms |
348 KB |
Output is correct |
| 9 |
Correct |
0 ms |
456 KB |
Output is correct |
| 10 |
Correct |
0 ms |
348 KB |
Output is correct |
| 11 |
Incorrect |
1 ms |
348 KB |
Breaking single line is causing network to disconnect. |
| 12 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
348 KB |
Output is correct |
| 2 |
Correct |
1 ms |
348 KB |
Output is correct |
| 3 |
Correct |
0 ms |
348 KB |
Output is correct |
| 4 |
Correct |
1 ms |
348 KB |
Output is correct |
| 5 |
Correct |
1 ms |
348 KB |
Output is correct |
| 6 |
Correct |
1 ms |
348 KB |
Output is correct |
| 7 |
Correct |
0 ms |
348 KB |
Output is correct |
| 8 |
Correct |
0 ms |
348 KB |
Output is correct |
| 9 |
Correct |
0 ms |
456 KB |
Output is correct |
| 10 |
Correct |
0 ms |
348 KB |
Output is correct |
| 11 |
Incorrect |
1 ms |
348 KB |
Breaking single line is causing network to disconnect. |
| 12 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Correct |
0 ms |
348 KB |
Output is correct |
| 2 |
Correct |
1 ms |
348 KB |
Output is correct |
| 3 |
Correct |
0 ms |
348 KB |
Output is correct |
| 4 |
Correct |
1 ms |
348 KB |
Output is correct |
| 5 |
Correct |
1 ms |
348 KB |
Output is correct |
| 6 |
Correct |
1 ms |
348 KB |
Output is correct |
| 7 |
Correct |
0 ms |
348 KB |
Output is correct |
| 8 |
Correct |
0 ms |
348 KB |
Output is correct |
| 9 |
Correct |
0 ms |
456 KB |
Output is correct |
| 10 |
Correct |
0 ms |
348 KB |
Output is correct |
| 11 |
Incorrect |
1 ms |
348 KB |
Breaking single line is causing network to disconnect. |
| 12 |
Halted |
0 ms |
0 KB |
- |
