Submission #331583

#	Time	Username	Problem	Language	Result	Execution time	Memory
331583		quindecim	Islands (IOI08_islands)	C++14	0 / 100	20 ms	23916 KiB

islands

#pragma GCC optimize ("Ofast")
#pragma GCC target ("avx2")
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const int MOD = 1e9+7;
const int MX = 1e6+10;
const ll INF = 0x3f3f3f3f3f3f3f3f;
#define int long long

int n, m, a[MX], w[MX];
vector<int> adj[MX];
ll ans, ret;
vector<ll> V, S;
bool vv[MX];

inline int cycle(int u) {
  if(vv[u]) return u;
  vv[u] = 1;
  int r = cycle(a[u]);
  if(r) {
    V.push_back(u);
    S.push_back(w[u]);
    if(r==u) return 0;
    else return r;
  }
  vv[u] = 0;
  return 0;
}

inline ll dfs(int u) {
  ll mx = 0;
  vv[u] = 1;
  for(int v : adj[u]) {
    if(!vv[v]) {
      ll r = dfs(v) + w[v];
      ret = max(ret, mx+r);
      mx = max(mx, r);
    }
  }
  return mx;
}

void solve(int u) {
  V.clear(); S.clear();
  cycle(u);
  reverse(V.begin(), V.end());
  reverse(S.begin(), S.end());
  for(auto &v : V) v = dfs(v);
  m = V.size();
  for(int i = m-1; i > 0; --i) swap(S[i], S[i-1]);
  for(int i = 1; i < m; ++i) S[i] += S[i-1];
  ll m1 = -INF, m2 = -INF;
  for(int i = 0; i < m; ++i) {
    ret = max(ret, max(m1+S[i]+V[i], m2-S[i]+V[i]+S[m-1]));
    m1 = max(m1, V[i]-S[i]);
    m2 = max(m2, V[i]+S[i]);
  }
}

signed main() {
  cin.tie(0)->sync_with_stdio(0);
  freopen("input.in", "r", stdin);
  cin >> n;
  for(int i = 1; i <= n; ++i) {
    cin >> a[i] >> w[i];
    adj[a[i]].push_back(i);
  }
  for(int i = 1; i <= n; ++i)
    if(!vv[i]) solve(i), ans+=ret, ret = 0;
  cout << ans << "\n";
  return 0;
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:63:10: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result]
   63 |   freopen("input.in", "r", stdin);
      |   ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 33
• Subtask 2: 0 / 3
• Subtask 3: 0 / 4
• Subtask 4: 0 / 10
• Subtask 5: 0 / 10
• Subtask 6: 0 / 10
• Subtask 7: 0 / 10
• Subtask 8: 0 / 10
• Subtask 9: 0 / 10