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const std = @import("std");
const Input = struct {
compressed: []Entry,
uncompressed: std.ArrayList(?u32),
const Entry = struct { taken: u8, free: u8 };
};
pub fn parse(allocator: std.mem.Allocator, data: []const u8) !Input {
var compressed = std.ArrayList(Input.Entry).init(allocator);
var i: usize = 0;
while (i < data.len) : (i += 2) {
try compressed.append(.{ .taken = data[i] - '0', .free = if (i + 1 == data.len or data[i + 1] == '\n') 0 else data[i + 1] - '0' });
}
var uncompressed = std.ArrayList(?u32).init(allocator);
for (0.., compressed.items) |j, entry| {
try uncompressed.appendNTimes(@intCast(j), entry.taken);
try uncompressed.appendNTimes(null, entry.free);
}
return .{ .compressed = compressed.items, .uncompressed = uncompressed };
}
const test_input = "2333133121414131402";
test "part1" {
var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
defer arena.deinit();
const output = try part1(arena.allocator(), try parse(arena.allocator(), test_input));
std.debug.print("got {}\n", .{output});
std.debug.assert(output == 1928);
}
pub fn part1(allocator: std.mem.Allocator, input: Input) !u64 {
var filesystem = std.ArrayList(u32).init(allocator);
var unmoved: u32 = 0;
var moved: u32 = @intCast(input.compressed.len);
var moved_left: u8 = 0;
while (unmoved < moved) {
try filesystem.appendNTimes(unmoved, input.compressed[unmoved].taken);
for (0..input.compressed[unmoved].free) |_| {
while (moved_left == 0) {
moved -= 1;
moved_left = input.compressed[moved].taken;
}
try filesystem.append(moved);
moved_left -= 1;
}
unmoved += 1;
}
try filesystem.appendNTimes(moved, moved_left);
// for (filesystem.items) |item| {
// std.debug.print("{}", .{item});
// }
// std.debug.print("\n", .{});
var sum: u64 = 0;
for (0.., filesystem.items) |pos, id| {
sum += pos * @as(u64, @intCast(id));
}
return sum;
}
test "part2" {
var arena = std.heap.ArenaAllocator.init(std.testing.allocator);
defer arena.deinit();
const output = try part2(arena.allocator(), try parse(arena.allocator(), test_input));
std.debug.print("got {}\n", .{output});
std.debug.assert(output == 2858);
}
pub fn part2(allocator: std.mem.Allocator, input: Input) !u32 {
var filesystem = std.ArrayList(u32).init(allocator);
_ = .{ filesystem, input };
filesystem = undefined;
var sum: u64 = 0;
for (0.., filesystem.items) |pos, id| {
sum += pos * @as(u64, @intCast(id));
}
return sum;
}
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