92 lines
2.2 KiB
C++
92 lines
2.2 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 <map>
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#include <set>
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#include <string>
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using LetterCountPair = std::pair<char, unsigned>;
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/**
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* \brief Ordering for LetterCount pairs
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*
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* This takes LetterCount pairs and orders them as defined in the puzzle. So higher counts come
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* first, followed by letters in alphabetical order.
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*/
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struct LetterCountOrder
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{
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constexpr auto operator()(LetterCountPair const& lhs, LetterCountPair const& rhs) const noexcept
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-> bool
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{
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if (lhs.second > rhs.second) {
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return true;
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}
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if (lhs.second == rhs.second) {
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return lhs.first < rhs.first;
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}
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return false;
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}
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};
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auto main() -> int
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{
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std::string line;
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std::uint64_t sum{0};
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while (std::getline(std::cin, line)) {
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std::map<char, unsigned> letter_counts;
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auto it{line.begin()};
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/* Iterate over the first part which we use to get the character counts. */
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while (std::isdigit(*it) == 0 && it != line.end()) {
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if (*it == '-') {
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it++;
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continue;
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}
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/* Insert or update the letter count for *it. */
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auto [lcit, success] = letter_counts.insert({*it, 1});
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if (!success) {
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lcit->second++;
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}
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++it;
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}
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/* Read the sector number. */
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assert(it != line.end());
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std::size_t idx{0};
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std::uint64_t sector_num{std::stoul(line.substr(it - line.begin()), &idx)};
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it += static_cast<std::ptrdiff_t>(idx);
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assert(*it == '[');
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++it;
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/* ordered_letters is the set of letter_counts ordered so that starting with begin() we get the
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* expected letters.
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*/
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std::set<LetterCountPair, LetterCountOrder> ordered_letters;
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for (auto lcit : letter_counts) {
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ordered_letters.insert(lcit);
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}
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/* Check that the checksum is what we want. */
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bool success = true;
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auto olit = ordered_letters.begin();
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while (success && *it != ']' && it != line.end()) {
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if (olit->first != *it) {
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success = false;
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}
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++it;
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++olit;
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}
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/* If success add to the sector sum. */
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if (success) {
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sum += sector_num;
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}
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}
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std::cout << "Sum of sector numbers: " << sum << '\n';
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return 0;
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}
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