Submission #1055424

#	Time	Username	Problem	Language	Result	Execution time	Memory
1055424		MilosMilutinovic	Islands (IOI08_islands)	C++14	80 / 100	210 ms	131072 KiB

islands

#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  vector<int> a(n), l(n);
  for (int i = 0; i < n; i++) {
    cin >> a[i] >> l[i];
    --a[i];
  }
  vector<vector<int>> g(n);
  for (int i = 0; i < n; i++) {
    g[i].push_back(a[i]);
    g[a[i]].push_back(i);
  }
  vector<bool> was(n);
  long long res = 0;
  vector<long long> d(n, -1);
  vector<vector<long long>> dp(n, vector<long long>(3));
  for (int i = 0; i < n; i++) {
    if (was[i]) {
      continue;
    }
    vector<int> que(1, i);
    for (int b = 0; b < (int) que.size(); b++) {
      int x = que[b];
      for (int y : g[x]) {
        if (!was[y]) {
          was[y] = true;
          que.push_back(y);
        }
      }
    }
    for (int x : que) {
      was[x] = false;
    }
    int x = i;
    while (!was[x]) {
      was[x] = true;
      x = a[x];
    }
    int y = a[x];
    vector<int> cyc(1, x);
    while (y != x) {
      cyc.push_back(y);
      y = a[y];
    }
    for (int x : que) {
      was[x] = true;
    }
    d[cyc[0]] = 0;
    for (int i = 1; i < (int) cyc.size(); i++) {
      int x = cyc[i - 1], y = cyc[i];
      d[y] = d[x] + l[x];
    }
    vector<int>().swap(que);
    function<void(int, int)> Solve = [&](int v, int pv) {
      for (int u : g[v]) {
        if (d[u] != -1 || u == pv) {
          continue;
        }
        Solve(u, v);
        dp[v][2] = max(dp[v][2], dp[u][2]);
        dp[v][2] = max(dp[v][2], dp[v][1] + dp[u][1] + l[u]);
        dp[v][1] = max(dp[v][1], dp[u][1] + l[u]);
      }
    };
    long long c = 0;
    for (int i : cyc) {
      Solve(i, i);
      c = max(c, dp[i][1]);
      c = max(c, dp[i][2]);
    }
    int sz = (int) cyc.size();
    vector<vector<long long>> mx(sz, vector<long long>(2, -(long long) 1e18));
    for (int i = sz - 1; i >= 0; i--) {
      if (i + 1 < sz) {
        mx[i] = mx[i + 1];
      }
      mx[i][0] = max(mx[i][0], d[cyc[i]] + dp[cyc[i]][1]);
      mx[i][1] = max(mx[i][1], -d[cyc[i]] + dp[cyc[i]][1]);
    }
    long long t = d[cyc.back()] + l[cyc.back()];
    for (int i = 0; i < sz; i++) {
      int low = i + 1, high = sz - 1, pos = i;
      while (low <= high) {
        int mid = (low + high) >> 1;
        if (t - (d[cyc[mid]] - d[cyc[i]]) >= (d[cyc[mid]] - d[cyc[i]])) {
          pos = mid;
          low = mid + 1;
        } else {
          high = mid - 1;
        }
      }
      if (pos + 1 < sz) {
        c = max(c, -d[cyc[i]] + dp[cyc[i]][1] + mx[pos + 1][0]);
      }
      if (pos > i) {
        c = max(c, t + d[cyc[i]] + dp[cyc[i]][1] + mx[i + 1][1]);
      }
    }
    res += c;
  }
  cout << res << '\n';
  return 0;
}

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