#include <bits/stdc++.h>
using namespace std;
using lint = long long;
using pil = pair<int, lint>;
const int MAX_N = 1e6 + 5;
int n;
vector<pil> adj[MAX_N];
bool seen[MAX_N];
vector<int> cyc;
bool in_cyc[MAX_N]; // In ANY of the cycles
vector<int> ord;
void dfs1(int u, int par = -1) {
seen[u] = true, ord.push_back(u);
bool par_seen = false;
for (pil x : adj[u]) {
int v = x.first;
if (v == par && !par_seen) { par_seen = true; continue; }
if (!seen[v]) { dfs1(v, u); continue; }
if (cyc.size()) continue;
int i = ord.size() - 1;
while (true) {
cyc.push_back(ord[i]), in_cyc[ord[i]] = true;
if (ord[i] == v) break;
i--;
}
}
ord.pop_back();
}
lint dp[MAX_N];
lint dfs2(int u, int par = -1) {
lint ans = 0;
priority_queue<lint> trans;
for (pil x : adj[u]) {
int v = x.first;
if (v == par || in_cyc[v]) continue;
ans = max(ans, dfs2(v, u));
dp[u] = max(dp[u], dp[v] + x.second);
trans.push(dp[v] + x.second);
}
lint new_ans = 0;
for (int i = 1; i <= 2; i++)
if (trans.size()) { new_ans += trans.top(); trans.pop(); }
ans = max(ans, new_ans);
return ans;
}
vector<lint> lens;
lint len_sum;
void precomp() {
if (cyc.size() == 2) {
set<int> lens_set;
for (int u : cyc) {
for (pil x : adj[u]) {
int v = x.first;
if (!in_cyc[v]) continue;
lens_set.insert(x.second);
}
}
lens.insert(lens.begin(), lens_set.begin(), lens_set.end());
len_sum = lens[0] + lens[1];
return;
}
for (int i = 0; i < cyc.size(); i++) {
int aft = (i + 1 == (int) cyc.size()) ? 0 : i + 1;
int u = cyc[i], v = cyc[aft];
for (pil x : adj[u])
if (x.first == v) lens.push_back(x.second), len_sum += x.second;
}
}
lint comp() {
vector<lint> pref_len = {0};
for (int i = 1; i < cyc.size(); i++)
pref_len.push_back(pref_len.back() + lens[i - 1]);
lint ans = 0;
for (int i = 0; i < cyc.size(); i++) {
for (int j = 0; j < cyc.size(); j++) {
if (i == j) continue;
int u = cyc[i], v = cyc[j];
lint diff = pref_len[j] - pref_len[i];
lint new_ans = (diff < 0) ? len_sum + diff + dp[u] + dp[v] : diff + dp[u] + dp[v];
// cout << u << " " << v << ": " << diff << " " << new_ans << endl;
ans = max(ans, new_ans);
}
}
return ans;
}
int main() {
// freopen("isl.in", "r", stdin), freopen("isl.out", "w", stdout);
cin >> n;
for (int u = 1; u <= n; u++) {
int v; cin >> v;
lint len; cin >> len;
adj[u].push_back({v, len}), adj[v].push_back({u, len});
}
lint ans = 0;
for (int u = 1; u <= n; u++) {
if (seen[u]) continue;
cyc.clear(), lens.clear(), len_sum = 0;
lint new_ans = 0;
dfs1(u);
for (int u : cyc) new_ans = max(new_ans, dfs2(u));
precomp();
// for (int i = 0; i < cyc.size(); i++) {
// cout << cyc[i] << " " << lens[i] << endl;
// }
new_ans = max(new_ans, comp());
reverse(cyc.begin(), cyc.end()), reverse(lens.begin(), next(lens.end(), -1));
new_ans = max(new_ans, comp());
ans += new_ans;
}
cout << ans << '\n';
}
Compilation message
islands.cpp: In function 'void precomp()':
islands.cpp:68:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
68 | for (int i = 0; i < cyc.size(); i++) {
| ~~^~~~~~~~~~~~
islands.cpp: In function 'lint comp()':
islands.cpp:78:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
78 | for (int i = 1; i < cyc.size(); i++)
| ~~^~~~~~~~~~~~
islands.cpp:82:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
82 | for (int i = 0; i < cyc.size(); i++) {
| ~~^~~~~~~~~~~~
islands.cpp:83:27: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
83 | for (int j = 0; j < cyc.size(); j++) {
| ~~^~~~~~~~~~~~
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
4 ms |
27224 KB |
Output is correct |
| 2 |
Correct |
4 ms |
27228 KB |
Output is correct |
| 3 |
Correct |
5 ms |
27392 KB |
Output is correct |
| 4 |
Correct |
4 ms |
27228 KB |
Output is correct |
| 5 |
Correct |
6 ms |
27384 KB |
Output is correct |
| 6 |
Correct |
4 ms |
27228 KB |
Output is correct |
| 7 |
Correct |
4 ms |
27384 KB |
Output is correct |
| 8 |
Correct |
4 ms |
27228 KB |
Output is correct |
| 9 |
Correct |
5 ms |
27228 KB |
Output is correct |
| 10 |
Correct |
4 ms |
27228 KB |
Output is correct |
| 11 |
Correct |
5 ms |
27228 KB |
Output is correct |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
5 ms |
27484 KB |
Output is correct |
| 2 |
Correct |
5 ms |
27344 KB |
Output is correct |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
6 ms |
27484 KB |
Output is correct |
| 2 |
Correct |
18 ms |
27856 KB |
Output is correct |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
50 ms |
28900 KB |
Output is correct |
| 2 |
Correct |
859 ms |
31784 KB |
Output is correct |
| 3 |
Correct |
17 ms |
28760 KB |
Output is correct |
| 4 |
Correct |
11 ms |
27996 KB |
Output is correct |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
1319 ms |
33328 KB |
Output is correct |
| 2 |
Correct |
1559 ms |
36320 KB |
Output is correct |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
1599 ms |
43932 KB |
Output is correct |
| 2 |
Execution timed out |
2035 ms |
49052 KB |
Time limit exceeded |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Execution timed out |
2032 ms |
55692 KB |
Time limit exceeded |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Correct |
511 ms |
105740 KB |
Output is correct |
| 2 |
Runtime error |
889 ms |
131072 KB |
Execution killed with signal 9 |
| 3 |
Halted |
0 ms |
0 KB |
- |
| # |
결과 |
실행 시간 |
메모리 |
Grader output |
| 1 |
Runtime error |
529 ms |
131072 KB |
Execution killed with signal 9 |
| 2 |
Halted |
0 ms |
0 KB |
- |
