Submission #889529

#	Time	Username	Problem	Language	Result	Execution time	Memory
889529		MilosMilutinovic	Monochrome Points (JOI20_monochrome)	C++14	100 / 100	1010 ms	30580 KiB

monochrome

#include <bits/stdc++.h>

using namespace std;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  cin >> n;
  string s;
  cin >> s;
  string t = "";
  for (int i = 0; i < 2 * n; i++) {
    if (s[i] == 'B') {
      for (int j = 0; j < 2 * n; j++) {
        t += s[(i + j) % (2 * n)];
      }
      break;
    }
  }
  s = t;
  vector<int> a;
  vector<int> b;
  for (int i = 0; i < 2 * n; i++) {
    if (s[i] == 'B') {
      a.push_back(i);
    } else {
      b.push_back(i);
    }
  }
  vector<int> fenw(2 * n);
  auto Modify = [&](int x, int v) {
    while (x < 2 * n) {
      fenw[x] += v;
      x |= (x + 1);
    }
  }; 
  auto Query = [&](int x) {
    int v = 0;
    while (x >= 0) {
      v += fenw[x];
      x = ((x & (x + 1))) - 1;
    }
    return v;
  };
  auto GetSum = [&](int L, int R) {
    return Query(R) - Query(L - 1);
  };
  vector<vector<array<int, 3>>> qs(2 * n + 1);
  vector<int> to(2 * n + 1, -1);
  auto Solve = [&](int k) {
    for (int i = 0; i <= 2 * n; i++) {
      qs[i].clear();
      to[i] = -1;
    }
    for (int i = 0; i < n; i++) {
      int L = a[i];
      int R = b[(i + k) % n];
      to[L] = R;
      if (L <= R) {
        qs[L].push_back({0, L - 1, -1});
        qs[L].push_back({R + 1, 2 * n - 1, -1});
        qs[R].push_back({0, L - 1, +1});
        qs[R].push_back({R + 1, 2 * n - 1, +1});
      } else {
        swap(L, R);
        qs[L].push_back({L + 1, R - 1, +1});
        qs[R].push_back({L + 1, R - 1, -1});
        qs[2 * n].push_back({L + 1, R - 1, +1});
      }
    }
    for (int i = 0; i < 2 * n; i++) {
      fenw[i] = 0;
    }
    long long ret = 0;
    for (int i = 0; i <= 2 * n; i++) {
      for (auto& p : qs[i]) {
        if (p[0] <= p[1]) {
          ret += GetSum(p[0], p[1]) * p[2];
        }
      }
      if (to[i] != -1) {
        Modify(to[i], 1);
      }
    }
    return ret;
  };
  int low = 0, high = n - 2;
  long long ans = Solve(n - 1);
  while (low <= high) {
    int mid = low + high >> 1;
    long long a = Solve(mid);
    long long b = Solve(mid + 1);
    ans = max(ans, a);
    ans = max(ans, b);
    if (a > b) {
      high = mid - 1;
    }  else {
      low = mid + 2;
    }
  }
  cout << ans << '\n';
  return 0;
}

Compilation message (stderr)

monochrome.cpp: In function 'int main()':
monochrome.cpp:91:19: warning: suggest parentheses around '+' inside '>>' [-Wparentheses]
   91 |     int mid = low + high >> 1;
      |               ~~~~^~~~~~

• Subtask 1: 4 / 4
• Subtask 2: 21 / 21
• Subtask 3: 10 / 10
• Subtask 4: 65 / 65