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132 lines
3.7 KiB
C++
132 lines
3.7 KiB
C++
#include <algorithm>
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#include <cstdint>
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#include <iostream>
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#include <list>
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#include <map>
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#include <string>
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#include <string_view>
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#include <tuple>
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static const std::map<char, const char *> hexToBin = {
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{'0', "0000"}, {'1', "0001"}, {'2', "0010"}, {'3', "0011"},
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{'4', "0100"}, {'5', "0101"}, {'6', "0110"}, {'7', "0111"},
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{'8', "1000"}, {'9', "1001"}, {'A', "1010"}, {'B', "1011"},
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{'C', "1100"}, {'D', "1101"}, {'E', "1110"}, {'F', "1111"}
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};
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static std::pair<uint64_t, std::string_view> solve(std::string_view packet);
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int main(int argc, const char *argv[])
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{
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if (argc != 2)
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return -1;
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std::string packetBin;
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std::string packetHex (argv[1]);
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for (char c : packetHex)
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packetBin += hexToBin.at(c);
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std::cout << solve(packetBin).first << std::endl;
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return 0;
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}
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uint64_t binStrToInt(std::string_view bin)
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{
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uint64_t n = 0;
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for (char c : bin) {
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n = n * 2ull;
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if (c == '1')
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++n;
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}
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return n;
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}
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bool isEmptyPacket(std::string_view packet)
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{
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return packet.empty() ||
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std::all_of(packet.cbegin(), packet.cend(),
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[](char c) { return c == '0'; });
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}
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std::pair<uint64_t, std::string_view> solve(std::string_view packet)
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{
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// Remove version
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packet = packet.substr(3);
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// Pull type ID
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const auto typeId = packet.substr(0, 3);
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packet = packet.substr(3);
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if (typeId == "100") {
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std::string numberStr;
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while (1) {
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const auto chunk = packet.substr(0, 5);
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packet = packet.substr(5);
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numberStr += chunk.substr(1);
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if (chunk.front() == '0')
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break;
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}
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return {binStrToInt(numberStr), isEmptyPacket(packet) ? "" : packet};
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} else {
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const bool isLengthBits = packet.front() == '0';
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packet = packet.substr(1);
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const auto lengthStr = packet.substr(0, isLengthBits ? 15 : 11);
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const auto length = binStrToInt(lengthStr);
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packet = packet.substr(isLengthBits ? 15 : 11);
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std::list<uint64_t> args;
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if (isLengthBits) {
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auto rem = packet.substr(0, length);
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while (1) {
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const auto ret = solve(rem);
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args.emplace_front(ret.first);
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if (ret.second.empty() || isEmptyPacket(ret.second))
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break;
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rem = ret.second;
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}
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packet = packet.substr(length);
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} else {
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for (uint64_t i = 0; i < length; ++i) {
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const auto ret = solve(packet);
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args.emplace_front(ret.first);
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packet = ret.second;
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if (isEmptyPacket(packet))
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break;
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}
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}
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uint64_t result;
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if (typeId == "000") {
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result = 0;
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for (auto a : args)
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result += a;
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} else if (typeId == "001") {
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result = 1;
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for (auto a : args)
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result *= a;
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} else if (typeId == "010") {
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result = *std::min_element(args.cbegin(), args.cend());
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} else if (typeId == "011") {
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result = *std::max_element(args.cbegin(), args.cend());
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} else if (typeId == "101") {
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const auto a1 = args.back();
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args.pop_back();
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result = args.back() < a1;
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} else if (typeId == "110") {
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const auto a1 = args.back();
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args.pop_back();
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result = args.back() > a1;
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} else if (typeId == "111") {
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const auto a1 = args.back();
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args.pop_back();
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result = args.back() == a1;
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}
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return {result, isEmptyPacket(packet) ? "" : packet};
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}
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}
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