Submission #284443

#	Time	Username	Problem	Language	Result	Execution time	Memory
284443		Haunted_Cpp	Islands (IOI08_islands)	C++17	73 / 100	1634 ms	131072 KiB

islands

/**
 *  author: Haunted_Cpp
**/
 
#include <bits/stdc++.h>
using namespace std;
 
#pragma GCC optimize("Ofast")
#pragma GCC target("fma,sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#pragma GCC optimize("unroll-loops")
 
template<typename T> ostream &operator << (ostream &os, const vector<T> &v) { os << '{'; string sep; for (const auto &x : v) os << sep << x, sep = ", "; return os << '}'; }
template<typename T, size_t size> ostream &operator << (ostream &os, const array<T, size> &arr) { os << '{'; string sep; for (const auto &x : arr) os << sep << x, sep = ", "; return os << '}'; }
template<typename A, typename B> ostream &operator << (ostream &os, const pair<A, B> &p) { return os << '(' << p.first << ", " << p.second << ')'; }
 
void debug_out() { cerr << endl; }
template<typename Head, typename... Tail> void debug_out(Head H, Tail... T) { cerr << ' ' << H; debug_out(T...); }
 
#ifdef LOCAL
#define debug(...) cerr << "(" << #__VA_ARGS__ << "):", debug_out(__VA_ARGS__)
#else
#define debug(...) 47
#endif
 
typedef long long i64;
 
const int MAX_N = 1e6 + 5;
 
vector<vector<int>> g(MAX_N);
 
int Time = 0, cycle_start, cycle_end;
 
vector<int> nxt(MAX_N), cost(MAX_N), par(MAX_N), cycle;

bitset<MAX_N> stack_status;
bitset<MAX_N> is_done;
bitset<MAX_N> is_cycle;

void find_cycle(int node, int p) {
  stack_status[node] = 1;
  for (auto et : g[node]) {
    if (et == p && !(nxt[p] == node && nxt[node] == p)) continue;
    if (stack_status[et] == 0) {
     par[et] = node;
     find_cycle(et, node);
    } else if (!is_done[et] && stack_status[et] == 1) {
      cycle_start = et;
      cycle_end = node;
    }
  }
  is_done[node] = 1;
}
 
int root;
 
pair<i64, int> dfs(int node, int p) {
  pair<i64, int> best_way = {0, node};
  for (auto et : g[node]) {
    const int w = (nxt[node] == et ? cost[node] : cost[et]);
    if (et != root && is_cycle[et]) continue;
    if (et != p) {
      pair<i64, int> cur = dfs(et, node);
      cur.first += w;
      best_way = max(best_way, cur);
    }
  } 
  return best_way;
}
 
i64 get_depth(int node, int p) {
  i64 mx = 0;
  for (auto et : g[node]) {
    const int w = (nxt[node] == et ? cost[node] : cost[et]);
    if (is_cycle[et]) continue;
    if (et != p) {
      mx = max(mx, w + get_depth(et, node));
    }
  }
  return mx;
}

int main() {
  ios::sync_with_stdio(0);
  cin.tie(0); 
  int n;
  cin >> n;
  for (int st = 0; st < n; st++) {
    int et, w;
    cin >> et >> w;
    --et;
    nxt[st] = et;
    cost[st] = w;
    g[st].emplace_back(et);
    g[et].emplace_back(st);
  }
  i64 ans = 0;
  for (int i = 0; i < n; i++) {
    if (stack_status[i] != 0) continue;
    cycle.clear();
    find_cycle(i, -1);
    i64 cycle_cost = 0;
    for (int cur = cycle_end; cur != cycle_start; cur = par[cur]) {
      cycle.emplace_back(cur);
      is_cycle[cur] = 1;
    }
    is_cycle[cycle_start] = 1;
    cycle.emplace_back(cycle_start);
    reverse(cycle.begin(), cycle.end());
    for (int j = 1; j < (int) cycle.size(); j++) {
      const int st = cycle[j - 1];
      const int et = cycle[j];
      const int w = (nxt[st] == et ? cost[st] : cost[et]);
      cycle_cost += w;
    }
    cycle_cost += (nxt[cycle.back()] == cycle[0] ? cost[cycle.back()] : cost[0]);
    debug(cycle_cost);
    i64 res = 0;
    for (auto to : cycle) {
      root = to;
      pair<i64, int> best_way = dfs(root, -1);
      res = max(res, dfs(best_way.second, -1).first);
    }
    i64 ccw = get_depth(cycle[0], -1); 
    i64 cw = get_depth(cycle[0], -1); 
    i64 start = 0;
    for (int j = 1; j < (int) cycle.size(); j++) {
      const int st = cycle[j - 1];
      const int et = cycle[j];
      const int w = (nxt[st] == et ? cost[st] : cost[et]);
      start += w;
      res = max(res, cw + start + get_depth(et, -1));
      cw = max(cw, -start + get_depth(et, -1));
      const i64 other = cycle_cost - start;
      res = max(res, ccw + other + get_depth(et, -1));
      ccw = max(ccw, start + get_depth(et, -1));
    }
    res = max({res, cw, ccw});
    ans += res;
  }
  cout << ans << '\n';
  return 0;
}

Compilation message (stderr)

islands.cpp: In function 'int main()':
islands.cpp:22:20: warning: statement has no effect [-Wunused-value]
   22 | #define debug(...) 47
      |                    ^~
islands.cpp:116:5: note: in expansion of macro 'debug'
  116 |     debug(cycle_cost);
      |     ^~~~~

• Subtask 1: 30 / 33
• Subtask 2: 3 / 3
• Subtask 3: 0 / 4
• Subtask 4: 0 / 10
• Subtask 5: 10 / 10
• Subtask 6: 10 / 10
• Subtask 7: 10 / 10
• Subtask 8: 10 / 10
• Subtask 9: 0 / 10