101 lines
2.7 KiB
C++
101 lines
2.7 KiB
C++
#include <array>
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#include <cassert>
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#include <iostream>
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#include <string>
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/** \brief Return the position described by BSP in s.
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* \tparam L2 log2 of the max position.
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* \tparam LOWER character which means use lower half.
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* \tparam UPPER character which means use upper half.
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* \param s String to parse, must be L2 characters long
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* \return Position described by s.
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*
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* \subsection After the fact commentary:
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*
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* We don't need to keep a record of high at all so the original solution
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* was over enthusiastic.
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*/
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template<unsigned L2, char LOWER, char UPPER>
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unsigned find_pos(std::string const& s)
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{
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assert(s.length() == L2);
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unsigned low = 0;
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unsigned width = 1 << (L2 - 1);
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for (auto c : s) {
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assert(width != 0);
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if (c == UPPER) {
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low = low + width;
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}
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else {
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assert(c == LOWER);
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}
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width >>= 1;
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}
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assert(width == 0);
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return low;
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}
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/** \brief A seat
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* \tparam L2R log 2 number of rows
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* \tparam L2C log 2 number of columns
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*/
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template<unsigned L2R, unsigned L2C>
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struct Seat
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{
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/** \brief Construct the seat.
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* \param s String representing seat location, must be L2R + L2C chars.
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*
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* First L2R characters must be 'F' and 'B' representing row, last L2C
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* characters must by 'L', and 'R' representing column.
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*
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* \brief After the fact commentary:
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*
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* Should have used initialiser lists.
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*/
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Seat(std::string const& s)
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: row_(find_pos<L2R, 'F', 'B'>(s.substr(0, L2R))),
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col_(find_pos<L2C, 'L', 'R'>(s.substr(L2R, L2C)))
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{
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assert(s.length() == L2R + L2C);
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std::cout << s << ": row " << row_ << ", column " << col_ << ", seat ID " << id() << ".\n";
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}
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/** Get seat ID. */
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unsigned id() const noexcept { return row_ * (1 << L2C) + col_; }
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unsigned row_; ///< Seat row
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unsigned col_; ///< Seat column
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};
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/** \brief main
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*
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* \subsection After the fact commentary:
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*
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* Could have initialised the array better.
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*/
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int main(int argc, char** argv)
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{
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constexpr unsigned l2r = 7; ///< Log 2 number of rows
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constexpr unsigned l2c = 3; ///< Log 2 number of columns
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constexpr unsigned max_id = 1 << (l2r + l2c); ///< Max ID.
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std::array<bool, max_id> id_present = {}; ///< Is the ID present?
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// Read the lines in marking IDs that are present
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for (std::string line; std::getline(std::cin, line);) {
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Seat<l2r, l2c> seat(line);
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assert(seat.id() < max_id);
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id_present[seat.id()] = true;
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}
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// We have an empty seat if it's ID is not present, but the IDs at +/-1 are.
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for (unsigned id = 1; id < id_present.size() - 1; ++id) {
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if (!id_present[id] && id_present[id - 1] && id_present[id + 1]) {
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std::cout << "Empty seat at: " << id << "\n";
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}
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}
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return 0;
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} |