87 lines
1.8 KiB
C++
87 lines
1.8 KiB
C++
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#include <algorithm>
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#include <bitset>
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#include <cstdint>
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#include <iostream>
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#include <sstream>
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#include <iterator>
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#include <vector>
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#include <doctest.h>
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#include <aocpp/Startup.hpp>
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namespace {
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auto Parse(std::istream & in) -> std::vector<std::int64_t>
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{
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std::vector<int64_t> result;
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std::int64_t x;
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while (in >> x) {
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result.push_back(x);
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}
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return result;
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}
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auto Part1(std::vector<std::int64_t> entries) {
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std::bitset<2020> numbers;
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std::sort(entries.begin(), entries.end());
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for (auto const i : entries) {
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if (i >= 2020) {
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break;
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}
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numbers.set(i);
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}
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for (auto const i : entries) {
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if (numbers.test(2020 - i)) {
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return (2020 - i) * i;
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}
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}
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throw std::runtime_error{"no part 1 solution"};
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}
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auto Part2(std::vector<std::int64_t> entries) {
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std::bitset<2020> numbers;
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std::sort(entries.begin(), entries.end());
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for (auto const i : entries) {
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if (i >= 2020) { break; }
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if (i < 2020) { numbers.set(i); }
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}
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for (auto it1 = entries.begin(); it1 != entries.end(); it1++) {
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for (auto it2 = std::next(it1); it2 != entries.end(); it2++) {
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auto target = 2020 - (*it1) - (*it2);
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if (target < 0) break;
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if (target < 2020 && numbers.test(target)) { return target * *it1 * *it2;}
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}
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}
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throw std::runtime_error{"no part 2 solution"};
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}
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}
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TEST_SUITE("documented examples") {
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std::istringstream in {
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"1721\n"
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"979\n"
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"366\n"
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"299\n"
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"675\n"
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"1456\n"};
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auto entries = Parse(in);
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TEST_CASE("part 1") {
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REQUIRE(Part1(entries) == 514579);
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}
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TEST_CASE("part 2") {
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REQUIRE(Part2(entries) == 241861950);
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}
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}
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auto main(int argc, char** argv) -> int {
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auto entries = Parse(aocpp::Startup(argc, argv));
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std::cout << "Part 1: " << Part1(entries) << std::endl;
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std::cout << "Part 2: " << Part2(entries) << std::endl;
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}
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