Submission #782398

#	Time	Username	Problem	Language	Result	Execution time	Memory
782398		tvladm2009	Monochrome Points (JOI20_monochrome)	C++17	100 / 100	930 ms	8104 KiB

monochrome

#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
const int N = (int) 2e5 + 7;
int n;
int aib[2 * N];
vector<int> v[2];
string s;

void update(int x) {
  x++;
  for (int i = x; i < 2 * N; i += i & -i) {
    aib[i]++;
  }
}

int query(int x) {
  x++;
  int ret = 0;
  for (int i = x; i >= 1; i -= i & -i) {
    ret += aib[i];
  }
  return ret;
}

int get(int l, int r) {
  return query(r) - query(l);
}

ll solve(int offset) {
  for (int i = 1; i <= 2 * n; i++) {
    aib[i] = 0;
  }
  vector<pair<int, int>> seg;
  for (int i = 0; i < n; i++) {
    int j = (i + offset) % n;
    seg.push_back({v[0][i], v[1][j]});
    if (seg.back().first > seg.back().second) {
      swap(seg.back().first, seg.back().second);
    }
  }
  sort(seg.begin(), seg.end());
  ll ret = 0;
  for (auto &it : seg) {
    ret += get(it.first, it.second);
    update(it.second);
  }
  return ret;
}

int main() {
  ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);

  ///freopen("input", "r", stdin);

  cin >> n >> s;
  for (int i = 0; i < 2 * n; i++) {
    v[(s[i] == 'B')].push_back(i);
  }

  int low = 0, high = n - 1, sol = 0;
  while (low < high) {
    int mid = (low + high) / 2;
    if (solve(mid) < solve(mid + 1)) {
      low = mid + 1;
    } else {
      high = mid;
    }
  }
  cout << solve(low) << "\n";
  return 0;
}

Compilation message (stderr)

monochrome.cpp: In function 'int main()':
monochrome.cpp:63:30: warning: unused variable 'sol' [-Wunused-variable]
   63 |   int low = 0, high = n - 1, sol = 0;
      |                              ^~~

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