Submission #1251508

#	Time	Username	Problem	Language	Result	Execution time	Memory
1251508		flashmt	Triple Peaks (IOI25_triples)	C++20	51 / 100	2099 ms	109492 KiB

triples

#include "triples.h"
#include <bits/stdc++.h>
#ifdef LOCAL
#include "Debug.h"
#else
#define debug(...) 42
#endif
using namespace std;
const int N = 2e5 + 5;
const int K = 650;

unordered_set<int> s[N * 3];

long long calcTriangle(vector<int> h)
{
  int n = size(h);
  vector<vector<int>> a(n * 3);
  vector<pair<int, int>> edges;
  for (int i = 0; i < n * 3; i++)
  {
    s[i].clear();
    a[i].clear();
  }
  for (int i = 0; i < n; i++)
  {
    int l = i - h[i], r = i + h[i];
    a[l + n].push_back(r + n);
    a[r + n].push_back(l + n);
    s[l + n].insert(r + n);
    s[r + n].insert(l + n);
    edges.push_back({l + n, r + n});
  }

  long long res = 0;
  vector<int> flag(n * 3, -1);
  for (int x = 0; x < n * 3; x++)
    if (size(a[x]) >= K)
    {
      for (int y : a[x])
        flag[y] = x;
      for (auto [y, z] : edges)
        if (flag[y] == x && flag[z] == x)
          res++;
    }
    else
    {
      for (int i = 0; i < size(a[x]); i++)
        for (int j = i + 1; j < size(a[x]); j++)
            if (s[a[x][i]].count(a[x][j]))
              res++;
    }

  assert(res % 3 == 0);
  return res / 3;
}

long long calc(vector<int> h)
{
  int n = size(h);
  vector<int> l(n), r(n);
  for (int i = 0; i < n; i++)
  {
    l[i] = i - h[i];
    r[i] = i + h[i];
  }

  long long res = 0;
  for (int i = 0; i < n; i++)
  {
    int j = r[i];
    if (j < n)
    {
      // 2.3..5
      res += r[j] < n && h[r[j]] == h[i] + h[j];

      // 2.5..3
      if (h[j] > h[i])
      {
        int k = j + h[j] - h[i];
        if (k < n && l[k] == j)
          res++;
      }

      // 5.3..2
      if (h[j] < h[i])
      {
        int k = i + h[j];
        if (r[k] == j && h[k] != h[j]) // exclude 211
          res++;
      }
    }
  }

  for (int i = 0; i < n; i++)
  {
    int j = l[i];
    if (j < 0)
      continue;

    // 5.2..3
    if (l[j] >= 0 && h[l[j]] == h[i] + h[j])
      res++;

    // 3.2..5
    int k = i + h[j];
    if (r[j] != i && k < n && h[k] == h[i] + h[j]) // exclude 112
      res++;
  }

  // k.2.i5.3..j
  res += calcTriangle(h);
  // exclude 121
  for (int i = 0; i < n; i++)
    if (h[i] % 2 == 0)
    {
      int u = i - h[i] / 2, v = i + h[i] / 2;
      if (u >= 0 && h[u] == h[i] / 2 && v < n && h[v] == h[i] / 2)
        res--;
    }

  return res;
}

long long count_triples(vector<int> h) {
  return calc(h);
}

vector<int> construct_range(int M, int K) {
  return {1, 1, 1};
}

• Subtask 0: 0 / 0
• Subtask 1: 8 / 8
• Subtask 2: 6 / 6
• Subtask 3: 10 / 10
• Subtask 4: 11 / 11
• Subtask 5: 16 / 16
• Subtask 6: 0 / 19
• Subtask 7: 0 / 5
• Subtask 8: 0 / 5
• Subtask 9: 0 / 5
• Subtask 10: 0 / 5
• Subtask 11: 0 / 5
• Subtask 12: 0 / 5