#include <bits/stdc++.h>
#define fi first
#define se second
using namespace std;
const int N = 1e6 + 11;
vector<pair<int, int>> G[N];
int p[N], w[N], de[N];
long long dp[N];
bool vis[N], cyc[N];
struct edge{
int u, v, w;
};
vector<edge> extra;
int tin[N], tout[N], t = 0;
void dfs(int id, int v, int pa = -1){
vis[v] = true; tin[v] = ++t;
for(auto i : G[v]){
if(!vis[i.fi]){
de[i.fi] = de[v] + 1;
p[i.fi] = v;
dfs(id, i.fi, v);
w[i.fi] = i.se;
}else if(i.fi != pa){
extra[id] = {v, i.fi, i.se};
}
}
tout[v] = t;
}
bool is_anc(int u, int v){
return tin[u] <= tin[v] && tout[v] <= tout[u];
}
long long ans[N];
void dfs_dp(int id, int v, int pa = -1){
vector<long long> dis;
for(auto i : G[v]){
if(!cyc[i.fi] && i.fi != pa){
dfs_dp(id, i.fi, v);
dis.push_back(dp[i.fi] + i.se);
}
}
sort(dis.begin(), dis.end());
if(dis.size() >= 2) ans[id] = max(ans[id], dis.back() + dis[dis.size() - 2]);
if(dis.size()) dp[v] = dis.back(), ans[id] = max(ans[id], dis.back());
}
void solve(int id, vector<long long> DP, vector<long long> W){
int n = W.size();
vector<long long> S(n * 2 + 1);
S[0] = 0;
for(int i = 0; i < n; i++){
S[i + 1] = S[i] + W[i];
}
for(int i = 0; i < n; i++){
S[n + i + 1] = S[n + i] + W[i];
}
priority_queue<long long> pq, _pq;
for(int i = 0; i < n; i++){
pq.push(S[i] + DP[i]);
}
for(int i = 0; i < n; i++){
_pq.push(S[i] + DP[i]);
while(pq.size() && _pq.size() && pq.top() == _pq.top()) pq.pop(), _pq.pop();
ans[id] = max(ans[id], DP[i] - S[i] + pq.top());
pq.push(S[i + n] + DP[i]);
}
}
int32_t main(){
cin.tie(0); cout.tie(0)->sync_with_stdio(false);
int n; cin >> n;
for(int i = 1; i <= n; i++){
int v, _w; cin >> v >> _w;
G[i].push_back({v, _w});
G[v].push_back({i, _w});
}
vector<int> roots;
for(int i = 1; i <= n; i++){
if(!vis[i]){
extra.resize(extra.size() + 1);
dfs(roots.size(), i);
roots.push_back(i);
}
}
int CC = roots.size();
for(int i = 0; i < CC; i++){
vector<pair<int, int>> cyc_L, cyc_R;
int x = extra[i].u, y = extra[i].v;
vector<int> cyc_v;
while(!is_anc(x, y)){
cyc_v.push_back(x);
cyc[x] = true;
cyc_L.push_back({x, w[x]});
x = p[x];
}
while(!is_anc(y, x)){
cyc_v.push_back(y);
cyc[y] = true;
cyc_R.push_back({y, w[y]});
y = p[y];
}
int l = x;
cyc_v.push_back(l);
cyc[l] = true;
for(auto v : cyc_v){
dfs_dp(i, v);
}
vector<long long> W, DP;
for(auto i : cyc_L){
DP.push_back(dp[i.fi]);
W.push_back(i.se);
}
DP.push_back(dp[l]);
for(int i = (int) cyc_R.size() - 1; i >= 0; i--){
V.push_back(cyc_R[i].fi);
DP.push_back(dp[cyc_R[i].fi]);
W.push_back(cyc_R[i].se);
}
W.push_back(extra[i].w);
solve(i, DP, W);
}
cout << accumulate(ans, ans + CC, 0LL) << endl;
}
Compilation message
islands.cpp: In function 'int32_t main()':
islands.cpp:122:4: error: 'V' was not declared in this scope
122 | V.push_back(cyc_R[i].fi);
| ^
