75 lines
2.3 KiB
C++
75 lines
2.3 KiB
C++
//
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// Created by Matthew Gretton-Dann on 03/12/2021.
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//
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#include <cassert>
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#include <iostream>
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#include <numeric>
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#include <string>
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#include <vector>
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/** \brief Convert the string s to a number
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* @param s String of 1s and 0s to convert
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* @return Value of string
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*/
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auto to_num(std::string const& s) -> std::uint64_t
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{
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std::uint64_t result{0};
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for (auto c : s) {
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assert(c == '1' || c == '0');
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result <<= 1;
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result |= (c == '1') ? 1 : 0;
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}
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return result;
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}
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/** \brief Find the rating for a given selector and set of lines.
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*
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* @tparam Fn Selector function type
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* @param lines Lines to select from
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* @param selector Takes bool saying whether ones are predominant, should return character to keep.
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* @return String of selected number.
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*/
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template<typename Fn>
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auto find_rating(std::vector<std::string> const& lines, Fn selector) -> std::string
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{
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/* Algorithm description: We copy the given lines and then for each index in the strings in turn
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* we see how many 1 digits are in that index. The function \a selector is then called to get the
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* character to keep, before erasing the strings we do not want to keep.
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*/
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std::vector<std::string> data{lines};
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assert(!data.empty());
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std::size_t len{data[1].size()};
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for (std::size_t i{0}; i < len; ++i) {
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auto one_bits{std::accumulate(
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data.begin(), data.end(), std::uint64_t{0},
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[i](std::uint64_t a, std::string const& s) { return a + (s[i] == '1' ? 1 : 0); })};
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char keep{selector(one_bits * 2 >= data.size())};
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auto it{std::remove_if(data.begin(), data.end(),
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[keep, i](std::string const& s) { return s[i] != keep; })};
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data.erase(it, data.end());
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if (data.size() <= 1) {
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break;
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}
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}
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assert(data.size() == 1);
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return data[0];
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}
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auto main() -> int
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{
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std::vector<std::string> lines;
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std::string line;
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while (std::getline(std::cin, line)) {
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lines.push_back(line);
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}
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auto oxygen_rating{
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to_num(find_rating(lines, [](bool mostly_ones) { return mostly_ones ? '1' : '0'; }))};
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auto co2_rating{
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to_num(find_rating(lines, [](bool mostly_ones) { return mostly_ones ? '0' : '1'; }))};
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std::cout << "Oxygen generator rating * CO2 scrubber rating = " << oxygen_rating << " * "
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<< co2_rating << " = " << oxygen_rating * co2_rating << '\n';
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return 0;
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} |