/*
for each connected component, find the simple path with maximum sum
consider the main cycle
each node of the main cycle has a tree hanging from it
-> ez trovare il path massimo nel tree
-> let f(i) be the maximum path hanging from the tree in i
choose i,j to maximize maxDistCycle(i,j) + f(i) + f(j)
start from a generic node v
keep two sets:
- L: {f(j) + dist_l(i, j)}
- R: {f(j) + dist_r(i, j)}
bias_l = bias_r = 0
ans = max(L.max() + bias_l, R.max + bias_r)
transition, from v to u (dx di v):
L,R.erase(u)
L,R.insert(v)
bias_l += L_{v,u}
bias_r -= L_{v,u}
transition #cycle times
*/
#include <bits/stdc++.h>
using namespace std;
using LL = long long;
#define watch(x) cerr << (#x) << " is " << x << endl
vector<bool> vis, cycle;
vector<array<LL, 2>> prv, nxt;
vector<LL> dl, dr;
vector<LL> f;
LL max_path(const vector<int>& c, const vector<vector<array<LL, 3>>>& adj) {
// identifica il ciclo
auto find_cycle = [&](auto&& self, int v, int pid = -1) -> bool {
if (vis[v]) return cycle[v] = true;
vis[v] = true;
for (auto [u, w, eid] : adj[v]) {
if (eid == pid) continue;
bool works = self(self, u, v);
if (works) {
nxt[v] = {u, w};
prv[u] = {v, w};
return cycle[v] ? false : cycle[v] = true;
}
}
return false;
};
find_cycle(find_cycle, c[0]);
auto path_in_tree = [&](auto&& self, int v, int pid = -1) -> LL {
LL ans = 0;
for (auto [u, w, eid] : adj[v]) {
if (cycle[u] || eid == pid) continue;
ans = max(ans, w + self(self, u, v));
}
return ans;
};
int start = -1;
for (int i : c) {
if (cycle[i]) {
start = i;
f[i] = path_in_tree(path_in_tree, i);
}
}
LL len = 0;
multiset<LL> L, R;
{
int v = start;
int u = start;
dl[v] = dr[u] = 0;
do {
auto [nv, lw] = nxt[v];
auto [nu, rw] = prv[u];
len += lw;
if (v != start) L.insert(f[v] + dl[v]);
if (u != start) R.insert(f[u] + dr[u]);
if (nv != start) dl[nv] = dl[v] + lw;
/*if (nu != start)*/ dr[nu] = dr[u] + rw;
v = nv;
u = nu;
} while (v != start && u != start); // should happen in the same moment
}
LL bias = 0;
LL ans = 0;
{
int v = start;
do {
// watch(v);
// watch(bias);
// cerr << "L: "; for (LL i : L) cerr << i << " "; cerr << endl;
// cerr << "R: "; for (LL i : R) cerr << i << " "; cerr << endl;
// cerr << endl;
ans = max(ans, *prev(L.end()) - bias + f[v]);
ans = max(ans, *prev(R.end()) + bias + f[v]);
int nv = nxt[v][0];
if (nv == start) break;
bias += nxt[v][1];
L.insert(f[v] + dl[v] + len);
R.insert(f[v] + dr[v] - len);
L.erase(L.find(f[nv] + dl[nv]));
R.erase(R.find(f[nv] + dr[nv]));
v = nv;
} while (v != start);
}
// cerr << ans << endl;
return ans;
}
int main() {
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
int n; cin >> n;
vector<vector<array<LL, 3>>> adj(n);
for (int i = 0; i < n; ++i) {
int a; cin >> a; --a;
int w; cin >> w;
adj[i].push_back({a, w, i});
adj[a].push_back({i, w, i});
}
vis.assign(n, false);
vector<vector<int>> cc;
auto dfs = [&](auto&& self, int v) -> void {
vis[v] = true;
cc.back().push_back(v);
for (auto [u, _, __] : adj[v]) {
if (!vis[u]) {
self(self, u);
}
}
};
for (int i = 0; i < n; ++i) {
if (!vis[i]) {
cc.push_back(vector<int>(0));
dfs(dfs, i);
}
}
f.assign(n, 0);
dl.assign(n, 1e18);
dr.assign(n, 1e18);
prv.assign(n, {-1,-1});
nxt.assign(n, {-1,-1});
vis.assign(n, false);
cycle.assign(n, false);
LL ans = 0;
for (const auto& c : cc) {
ans += max_path(c, adj);
}
cout << ans << "\n";
}
Compilation message
islands.cpp: In function 'int main()':
islands.cpp:118:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
118 | freopen("input.txt", "r", stdin);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
islands.cpp:119:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
119 | freopen("output.txt", "w", stdout);
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 2 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 3 |
Incorrect |
1 ms |
212 KB |
Output isn't correct |
| 4 |
Incorrect |
1 ms |
212 KB |
Output isn't correct |
| 5 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 6 |
Incorrect |
1 ms |
212 KB |
Output isn't correct |
| 7 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 8 |
Incorrect |
1 ms |
212 KB |
Output isn't correct |
| 9 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 10 |
Incorrect |
1 ms |
212 KB |
Output isn't correct |
| 11 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
1 ms |
212 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
1 ms |
212 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
1 ms |
212 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
0 ms |
212 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
| # |
Verdict |
Execution time |
Memory |
Grader output |
| 1 |
Incorrect |
1 ms |
212 KB |
Output isn't correct |
| 2 |
Halted |
0 ms |
0 KB |
- |
