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const std = @import("std");
const aoc = @import("aoc");
const Player = enum { P1, P2 };
const GameResult = struct { score: u64, winner: Player };
fn parseInput(input: []u8, decks: [2]*std.ArrayList(u32)) !void {
var partit = std.mem.split(u8, input, "\n\n");
var decknum: u32 = 0;
while (partit.next()) |part| : (decknum += 1) {
if (decknum == 2) break;
var lineit = std.mem.tokenize(u8, part, "\n");
_ = lineit.next();
while (lineit.next()) |line| {
try decks[decknum].append(try std.fmt.parseInt(u32, line, 10));
}
}
if (decknum < 2) return aoc.Error.InvalidInput;
}
fn printDeck(deck: *std.ArrayList(u32)) void {
for (deck.items) |v, i| {
if (i > 0) aoc.debugfmt(", ", .{});
aoc.debugfmt("{}", .{v});
}
}
fn printRoundInfo(roundnum: u32, decks: [2]*std.ArrayList(u32)) void {
aoc.debugfmt("\n-- ROUND {} --\n", .{roundnum});
aoc.debugfmt("Player 1's deck: ", .{});
printDeck(decks[0]);
aoc.debugfmt("\nPlayer 2's deck: ", .{});
printDeck(decks[1]);
aoc.debugfmt("\n", .{});
}
fn printPickedCards(card1: u32, card2: u32) void {
aoc.debugfmt("Player 1 plays: {}\n", .{card1});
aoc.debugfmt("Player 2 plays: {}\n", .{card2});
}
fn calcScore(deck: *std.ArrayList(u32)) u64 {
var score: u64 = 0;
for (deck.items) |v, i| {
score += v * (deck.items.len - i);
}
return score;
}
fn copyList(allocator: std.mem.Allocator, list: []u32) !std.ArrayList(u32) {
var newlist = std.ArrayList(u32).init(allocator);
errdefer newlist.deinit();
for (list) |v| {
try newlist.append(v);
}
return newlist;
}
fn part1Round(allocator: std.mem.Allocator, roundnum: u32, decks: [2]*std.ArrayList(u32)) anyerror!void {
_ = allocator;
if (aoc.debug) printRoundInfo(roundnum, decks);
const card1: u32 = decks[0].orderedRemove(0);
const card2: u32 = decks[1].orderedRemove(0);
if (aoc.debug) printPickedCards(card1, card2);
if (card1 > card2) {
if (aoc.debug) aoc.debugfmt("Player1 wins\n", .{});
try decks[0].append(card1);
try decks[0].append(card2);
} else if (card2 > card1) {
if (aoc.debug) aoc.debugfmt("Player2 wins\n", .{});
try decks[1].append(card2);
try decks[1].append(card1);
} else return aoc.Error.InvalidInput;
}
fn part2Round(
allocator: std.mem.Allocator,
roundnum: u32,
decks: [2]*std.ArrayList(u32),
) anyerror!void {
if (aoc.debug) printRoundInfo(roundnum, decks);
const card1: u32 = decks[0].orderedRemove(0);
const card2: u32 = decks[1].orderedRemove(0);
if (aoc.debug) printPickedCards(card1, card2);
var winner = @intToEnum(Player, @boolToInt(card2 > card1));
if (card1 <= decks[0].items.len and card2 <= decks[1].items.len) {
if (aoc.debug) aoc.debugfmt("\nStarting subgame..\n", .{});
var tmp_deck1 = try copyList(allocator, decks[0].items[0..card1]);
defer tmp_deck1.deinit();
var tmp_deck2 = try copyList(allocator, decks[1].items[0..card2]);
defer tmp_deck2.deinit();
const result = try playGame(allocator, [2]*std.ArrayList(u32){ &tmp_deck1, &tmp_deck2 }, part2Round);
winner = result.winner;
if (aoc.debug) {
const wp: u32 = if (winner == Player.P1) 1 else 2;
aoc.debugfmt("Player{} wins the subgame\n...anyway, back to previous game\n\n", .{wp});
}
}
if (winner == Player.P1) {
if (aoc.debug) aoc.debugfmt("Player1 wins the round\n", .{});
try decks[0].append(card1);
try decks[0].append(card2);
} else if (winner == Player.P2) {
if (aoc.debug) aoc.debugfmt("Player2 wins the round\n", .{});
try decks[1].append(card2);
try decks[1].append(card1);
} else return aoc.Error.InvalidInput;
}
fn playGame(
allocator: std.mem.Allocator,
decks: [2]*std.ArrayList(u32),
roundFunc: *const fn (
alloc: std.mem.Allocator,
num: u32,
decks: [2]*std.ArrayList(u32),
) anyerror!void,
) !GameResult {
var ctxstack = std.ArrayList(u64).init(allocator);
defer ctxstack.deinit();
var roundnum: u32 = 1;
while (decks[0].items.len > 0 and decks[1].items.len > 0) : (roundnum += 1) {
try roundFunc(allocator, roundnum, decks);
var hash: u64 = calcScore(decks[0]) + 100000 * calcScore(decks[1]);
if (std.mem.indexOfScalar(u64, ctxstack.items, hash) != null) {
return GameResult{ .score = calcScore(decks[0]), .winner = Player.P1 };
}
try ctxstack.append(hash);
}
var nonempty = if (decks[0].items.len != 0) decks[0] else decks[1];
return GameResult{
.score = calcScore(nonempty),
.winner = if (nonempty == decks[0]) Player.P1 else Player.P2,
};
}
fn part1(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
_ = args;
var deck1 = std.ArrayList(u32).init(allocator);
defer deck1.deinit();
var deck2 = std.ArrayList(u32).init(allocator);
defer deck2.deinit();
const decks = [2]*std.ArrayList(u32){ &deck1, &deck2 };
try parseInput(input, decks);
const result = try playGame(allocator, decks, part1Round);
return try std.fmt.allocPrint(allocator, "{}", .{result.score});
}
fn part2(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
_ = args;
var deck1 = std.ArrayList(u32).init(allocator);
defer deck1.deinit();
var deck2 = std.ArrayList(u32).init(allocator);
defer deck2.deinit();
const decks = [2]*std.ArrayList(u32){ &deck1, &deck2 };
try parseInput(input, decks);
const result = try playGame(allocator, decks, part2Round);
return try std.fmt.allocPrint(allocator, "{}", .{result.score});
}
pub const main = aoc.main(part1, part2, .{ "32272", "33206" });
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