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const std = @import("std");
const aoc = @import("aoc");
const SeatState = enum { EMPTY, FLOOR, TAKEN };
const MapDims = struct { width: usize, height: usize };
const Dir = struct { x: i8, y: i8 };
const Pos = struct { x: i128, y: i128 };
const adjacent = [_]Dir{
Dir{ .x = -1, .y = -1 },
Dir{ .x = -0, .y = -1 },
Dir{ .x = 1, .y = -1 },
Dir{ .x = -1, .y = 0 },
Dir{ .x = 1, .y = 0 },
Dir{ .x = -1, .y = 1 },
Dir{ .x = 0, .y = 1 },
Dir{ .x = 1, .y = 1 },
};
fn parseMap(mapitems: *[]SeatState, dims: *MapDims, input: []const u8, allocator: std.mem.Allocator) !void {
var lineit = std.mem.tokenize(u8, input, "\n");
var map = std.ArrayList(SeatState).init(allocator);
errdefer map.deinit();
while (lineit.next()) |line| {
if (dims.width == 0) {
dims.width = line.len;
} else if (dims.width != line.len) {
return aoc.Error.InvalidInput;
}
for (line) |c| {
try map.append(switch (c) {
'#' => SeatState.TAKEN,
'L' => SeatState.EMPTY,
'.' => SeatState.FLOOR,
else => {
return aoc.Error.InvalidInput;
},
});
}
dims.height += 1;
}
mapitems.* = map.toOwnedSlice();
}
fn printMap(mapitems: []SeatState, dims: MapDims) void {
for (mapitems) |state, i| {
const c: u8 = switch (state) {
SeatState.EMPTY => 'L',
SeatState.TAKEN => '#',
SeatState.FLOOR => '.',
};
if (i % dims.width == 0) {
aoc.debugfmt("\n", .{});
}
aoc.debugfmt("{c}", .{c});
}
}
fn simulateStrategyOne(before: []SeatState, after: []SeatState, dims: MapDims) u32 {
var seat_changes: u32 = 0;
for (before) |state, i| {
const p = Pos{ .x = i % dims.width, .y = i / dims.width };
var count: u32 = 0;
for (adjacent) |ap| {
if (p.x + ap.x >= dims.width or p.x + ap.x < 0 or p.y + ap.y >= dims.height or p.y + ap.y < 0) continue;
const ni = @intCast(u64, @intCast(i64, i) + ap.x + ap.y * @intCast(i64, dims.width));
count += @boolToInt(before[ni] == SeatState.TAKEN);
}
if (state == SeatState.EMPTY and count == 0) {
after[i] = SeatState.TAKEN;
seat_changes += 1;
} else if (state == SeatState.TAKEN and count >= 4) {
after[i] = SeatState.EMPTY;
seat_changes += 1;
} else {
after[i] = before[i];
}
}
return seat_changes;
}
fn simulateStrategyTwo(before: []SeatState, after: []SeatState, dims: MapDims) u32 {
var seat_changes: u32 = 0;
for (before) |state, i| {
const p = Pos{ .x = i % dims.width, .y = i / dims.width };
var count: u32 = 0;
for (adjacent) |ap| {
var iterp = Pos{ .x = p.x + ap.x, .y = p.y + ap.y };
while (iterp.x < dims.width and iterp.x >= 0 and iterp.y < dims.height and iterp.y >= 0) {
const ni = @intCast(u64, iterp.x + iterp.y * @intCast(i64, dims.width));
if (before[ni] == SeatState.TAKEN) {
count += 1;
break;
} else if (before[ni] == SeatState.EMPTY) {
break;
} else {
iterp.x += ap.x;
iterp.y += ap.y;
}
}
}
if (state == SeatState.EMPTY and count == 0) {
after[i] = SeatState.TAKEN;
seat_changes += 1;
} else if (state == SeatState.TAKEN and count >= 5) {
after[i] = SeatState.EMPTY;
seat_changes += 1;
} else {
after[i] = before[i];
}
}
return seat_changes;
}
fn part1(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
_ = args;
var mapdims = MapDims{ .width = 0, .height = 0 };
var mapitems: []SeatState = undefined;
try parseMap(&mapitems, &mapdims, input, allocator);
defer allocator.free(mapitems);
var mapresult = try allocator.alloc(SeatState, mapitems.len);
defer allocator.free(mapresult);
var round: u32 = 0;
while (simulateStrategyOne(mapitems, mapresult, mapdims) > 0) : (round += 1) {
aoc.debugfmt("\rRound: {}", .{round});
std.mem.copy(SeatState, mapitems, mapresult);
}
var taken_count: u64 = 0;
for (mapresult) |state| {
taken_count += @boolToInt(state == SeatState.TAKEN);
}
aoc.debugfmt("\nSeats Occupied: {}\n", .{taken_count});
return try std.fmt.allocPrint(allocator, "{d}", .{taken_count});
}
fn part2(allocator: std.mem.Allocator, input: []u8, args: [][]u8) !?[]u8 {
_ = args;
var mapdims = MapDims{ .width = 0, .height = 0 };
var mapitems: []SeatState = undefined;
try parseMap(&mapitems, &mapdims, input, allocator);
defer allocator.free(mapitems);
var mapresult = try allocator.alloc(SeatState, mapitems.len);
defer allocator.free(mapresult);
var round: u32 = 0;
while (simulateStrategyTwo(mapitems, mapresult, mapdims) > 0) : (round += 1) {
aoc.debugfmt("\rRound: {}", .{round});
std.mem.copy(SeatState, mapitems, mapresult);
}
var taken_count: u64 = 0;
for (mapresult) |state| {
taken_count += @boolToInt(state == SeatState.TAKEN);
}
aoc.debugfmt("\nSeats Occupied: {}\n", .{taken_count});
return try std.fmt.allocPrint(allocator, "{d}", .{taken_count});
}
pub const main = aoc.main(part1, part2, .{ "2126", "1914" });
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