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advent-of-code-2020
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Clean up day 16

master
Nick Krichevsky 2020-12-16 03:38:15 -05:00
parent 197cb30f95
commit 5c922f48d0
1 changed files with 91 additions and 23 deletions
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114
day16/day16.cpp
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@ -11,12 +11,16 @@
constexpr auto NEARBY_TICKETS_HEADER = "nearby tickets:";
constexpr auto YOUR_TICKET_HEADER = "your ticket:";
constexpr auto DEPARTURE_PREFIX = "departure";
constexpr auto FIELD_PATTERN = R"((.*): (\d+)-(\d+) or (\d+)-(\d+))";
// This has to be the grossest type signature I've written in a while, but it's of
// a-b or c-d maps to pair<a, b> or pair<c ,d>
using RangeSpec = std::pair<std::pair<int, int>, std::pair<int, int>>;
/**
* A field of the ticket
*/
class TicketField {
public:
TicketField(std::string &name, RangeSpec &ranges) : name(name), ranges(ranges) {
@ -47,6 +51,9 @@ class TicketField {
RangeSpec ranges;
};
/**
* The specification of all tickets from the puzzle input
*/
class TicketSpec {
public:
TicketSpec(
@ -88,6 +95,13 @@ std::vector<std::string> readInput(const std::string &filename) {
return input;
}
/**
* Parse the fields of the ticket specification
* @tparam Iter The type of iterator to get the fields from
* @param start The start iterator
* @param end The end iterator
* @return std::vector<TicketField> All of the ticket fields from the input
*/
template <typename Iter>
std::vector<TicketField> parseFields(Iter start, Iter end) {
std::vector<TicketField> fields;
@ -106,6 +120,11 @@ std::vector<TicketField> parseFields(Iter start, Iter end) {
return fields;
}
/**
* Parse a single ticket
* @param rawTicket The ticket to parse
* @return std::vector<int> The ticket's fields
*/
std::vector<int> parseTicket(const std::string &rawTicket) {
std::vector<int> ticket;
folly::split(",", rawTicket, ticket);
@ -113,6 +132,13 @@ std::vector<int> parseTicket(const std::string &rawTicket) {
return ticket;
}
/**
* Get all of the nearby tickets
* @tparam Iter The iterator type to get the nearby tickets
* @param start The start iterator
* @param end The end iterator
* @return std::vector<std::vector<int>> The nearby tickets and their fields
*/
template <typename Iter>
std::vector<std::vector<int>> parseNearbyTickets(Iter start, Iter end) {
std::vector<std::vector<int>> nearbyTickets;
@ -124,6 +150,11 @@ std::vector<std::vector<int>> parseNearbyTickets(Iter start, Iter end) {
return nearbyTickets;
}
/**
* Parse the puzzle input
* @param input The puzzle input
* @return TicketSpec The puzzle input as a TicketSpec
*/
TicketSpec parseInput(const std::vector<std::string> &input) {
auto fieldsEnd = std::find(input.cbegin(), input.cend(), "");
auto yourTicketBegin = std::find(input.cbegin(), input.cend(), YOUR_TICKET_HEADER);
@ -134,6 +165,14 @@ TicketSpec parseInput(const std::vector<std::string> &input) {
return TicketSpec(std::move(yourTicket), std::move(nearbyTickets), std::move(pairs));
}
/**
* Checks if a value is in range for all of the ticket's ranges
* @param value THe value to check
* @param ticketSpec The ticket specification to check against
* @return true If the value is valid
* @return false If the value is nto valid
*/
bool inRangesForTicket(int value, const TicketSpec &ticketSpec) {
return std::any_of(
ticketSpec.getFields().cbegin(), ticketSpec.getFields().cend(), [value](const TicketField &field) {
@ -141,6 +180,11 @@ bool inRangesForTicket(int value, const TicketSpec &ticketSpec) {
});
}
/**
* Get all of the valid tickets in the input
* @param ticketSpec The ticket spec from the input
* @return std::vector<std::vector<int>> The valid tickets
*/
std::vector<std::vector<int>> getValidTickets(const TicketSpec &ticketSpec) {
// There might be a nicer way than copying these but frankly I can't think of one that's clean.
std::vector<std::vector<int>> allTickets(ticketSpec.getOtherTickets());
@ -159,19 +203,12 @@ std::vector<std::vector<int>> getValidTickets(const TicketSpec &ticketSpec) {
return allTickets;
}
int part1(const TicketSpec &ticketSpec) {
return std::accumulate(
ticketSpec.getOtherTickets().cbegin(),
ticketSpec.getOtherTickets().cend(),
0,
[&ticketSpec](int total, const std::vector<int> &ticket) {
return total + std::accumulate(ticket.cbegin(), ticket.cend(), 0, [&ticketSpec](int subtotal, int field) {
return inRangesForTicket(field, ticketSpec) ? subtotal : subtotal + field;
});
});
}
long part2(const TicketSpec &ticketSpec) {
/**
* Generate candidates of what fields could possibly be used for each position in the tickets
* @param ticketSpec The ticket specification from the problem
* @return std::map<TicketField, std::set<int>> A map of the field candidates
*/
std::map<TicketField, std::set<int>> generateFieldCandidates(const TicketSpec &ticketSpec) {
auto validTickets = getValidTickets(ticketSpec);
std::map<TicketField, std::set<int>> fieldCandidates;
for (const TicketField &field : ticketSpec.getFields()) {
@ -186,6 +223,16 @@ long part2(const TicketSpec &ticketSpec) {
}
}
return fieldCandidates;
}
/**
* Determine which fields map to what positions in the tickets
* @param ticketSpec The ticket specification from the input
* @return std::map<TicketField, int> A mapping of fields to positions in the tickets
*/
std::map<TicketField, int> determineFieldPositions(const TicketSpec &ticketSpec) {
std::map<TicketField, std::set<int>> fieldCandidates = generateFieldCandidates(ticketSpec);
std::map<TicketField, int> fieldPositions;
for (auto candidate : fieldCandidates) {
std::set<int> valid = candidate.second;
@ -206,20 +253,41 @@ long part2(const TicketSpec &ticketSpec) {
valid = std::move(difference);
}
}
assert(valid.size() == 1);
fieldPositions.emplace(candidate.first, *valid.begin());
}
long total = 1;
for (const auto &fieldPosition : fieldPositions) {
auto fieldName = fieldPosition.first.getName();
if (fieldName.rfind("departure", 0) != 0) {
continue;
if (valid.size() != 1) {
throw new std::invalid_argument("Invalid input; not possible to determine the field mappings.");
}
total *= ticketSpec.getOurTicket().at(fieldPosition.second);
fieldPositions.emplace(candidate.first, *valid.begin());
}
return total;
return fieldPositions;
}
int part1(const TicketSpec &ticketSpec) {
return std::accumulate(
ticketSpec.getOtherTickets().cbegin(),
ticketSpec.getOtherTickets().cend(),
0,
[&ticketSpec](int total, const std::vector<int> &ticket) {
return total + std::accumulate(ticket.cbegin(), ticket.cend(), 0, [&ticketSpec](int subtotal, int field) {
return inRangesForTicket(field, ticketSpec) ? subtotal : subtotal + field;
});
});
}
long part2(const TicketSpec &ticketSpec) {
auto fieldPositions = determineFieldPositions(ticketSpec);
return std::accumulate(
fieldPositions.cbegin(),
fieldPositions.cend(),
1L,
[&ticketSpec](long total, std::pair<TicketField, int> fieldPosition) {
auto fieldName = fieldPosition.first.getName();
if (fieldName.rfind(DEPARTURE_PREFIX, 0) != 0) {
return total;
}
return total * ticketSpec.getOurTicket().at(fieldPosition.second);
});
}
int main(int argc, char *argv[]) {