Submission #307510

#	Time	Username	Problem	Language	Result	Execution time	Memory
307510		KoD	Monochrome Points (JOI20_monochrome)	C++17	100 / 100	63 ms	3684 KiB

monochrome

#line 1 "main.cpp"

/**
 * @title Template
 */

#include <iostream>
#include <algorithm>
#include <utility>
#include <numeric>
#include <vector>
#include <array>
#include <cassert>

#line 2 "/Users/kodamankod/Desktop/cpp_programming/Library/other/chmin_chmax.cpp"

template <class T, class U>
constexpr bool chmin(T &lhs, const U &rhs) {
  if (lhs > rhs) { lhs = rhs; return true; }
  return false;
}

template <class T, class U>
constexpr bool chmax(T &lhs, const U &rhs) {
  if (lhs < rhs) { lhs = rhs; return true; }
  return false;
}

/**
 * @title Chmin/Chmax
 */
#line 2 "/Users/kodamankod/Desktop/cpp_programming/Library/other/range.cpp"

#line 4 "/Users/kodamankod/Desktop/cpp_programming/Library/other/range.cpp"

class range {
public:
  class iterator {
  private:
    int64_t M_position;

  public:
    constexpr iterator(int64_t position) noexcept: M_position(position) { }
    constexpr void operator ++ () noexcept { ++M_position; }
    constexpr bool operator != (iterator other) const noexcept { return M_position != other.M_position; }
    constexpr int64_t operator * () const noexcept { return M_position; }
  };

  class reverse_iterator {
  private:
    int64_t M_position;
  
  public:
    constexpr reverse_iterator(int64_t position) noexcept: M_position(position) { }
    constexpr void operator ++ () noexcept { --M_position; }
    constexpr bool operator != (reverse_iterator other) const noexcept { return M_position != other.M_position; }
    constexpr int64_t operator * () const noexcept { return M_position; }
  };
  
private:
  const iterator M_first, M_last;

public:
  constexpr range(int64_t first, int64_t last) noexcept: M_first(first), M_last(std::max(first, last)) { }
  constexpr iterator begin() const noexcept { return M_first; }
  constexpr iterator end() const noexcept { return M_last; }
  constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator(*M_last - 1); } 
  constexpr reverse_iterator rend() const noexcept { return reverse_iterator(*M_first - 1); } 
};

/**
 * @title Range
 */
#line 2 "/Users/kodamankod/Desktop/cpp_programming/Library/other/rev.cpp"

#include <type_traits>
#include <iterator>
#line 6 "/Users/kodamankod/Desktop/cpp_programming/Library/other/rev.cpp"

template <class T>
class rev_impl {
public:
  using iterator = decltype(std::rbegin(std::declval<T>()));

private:
  const iterator M_begin;
  const iterator M_end;

public:
  constexpr rev_impl(T &&cont) noexcept: M_begin(std::rbegin(cont)), M_end(std::rend(cont)) { }
  constexpr iterator begin() const noexcept { return M_begin; }
  constexpr iterator end() const noexcept { return M_end; }
};

template <class T>
constexpr decltype(auto) rev(T &&cont) {
  return rev_impl<T>(std::forward<T>(cont));
}

/**
 * @title Reverser
 */
#line 17 "main.cpp"

using i32 = int32_t;
using i64 = int64_t;
using u32 = uint32_t;
using u64 = uint64_t;

constexpr i32 inf32 = (i32(1) << 30) - 1;
constexpr i64 inf64 = (i64(1) << 62) - 1;

int main() {
  std::ios_base::sync_with_stdio(false);
  std::cin.tie(nullptr);
  size_t N;
  std::cin >> N;
  std::vector<bool> color(2 * N);
  for (auto i: range(0, 2 * N)) {
    char c;
    std::cin >> c;
    color[i] = (c == 'B');
  }
  if (color[0]) {
    for (auto i: range(0, 2 * N)) {
      color[i] = !color[i];
    }
  }
  std::vector<i32> W, B;
  W.reserve(N);
  B.reserve(N);
  for (auto i: range(0, 2 * N)) {
    (color[i] ? B : W).push_back(i);
  }
  const auto solve = [&](const size_t K) {
    std::vector<i32> partner(2 * N);
    i64 sum = 0;
    for (auto i: range(0, N)) {
      const auto j = (i + K) % N;
      if (W[i] < B[j]) {
        sum += std::min<i32>(B[j] - W[i] - 1, 2 * N - (B[j] - W[i] + 1));
      }
      else {
        sum += std::min<i32>(W[i] - B[j] - 1, 2 * N - (W[i] - B[j] + 1));
      }
    }
    return sum / 2;
  };
  i64 ans = 0;
  i32 l = 0, r = N - 1;
  while (r - l > 2) {
    const auto m1 = (l + r) / 2;
    const auto m2 = m1 + 1;
    const auto v1 = solve(m1);
    const auto v2 = solve(m2);
    if (v1 < v2) {
      l = m1;
    }
    else {
      r = m2;
    }
  }
  for (auto k: range(l, r + 1)) {
    chmax(ans, solve(k));
  }
  std::cout << ans << '\n';
  return 0;
}

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