1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
|
const std = @import("std");
test {
std.debug.assert(try part1(
\\3 4
\\4 3
\\2 5
\\1 3
\\3 9
\\3 3
) == 11);
}
const Input = struct {
lefts: std.ArrayList(u32),
rights: std.ArrayList(u32),
};
pub fn parse(allocator: std.mem.Allocator, input: []const u8) !Input {
var lines = std.mem.split(u8, input, "\n");
var lefts = std.ArrayList(u32).init(allocator);
// defer lefts.deinit();
var rights = std.ArrayList(u32).init(allocator);
// defer rights.deinit();
while (lines.next()) |line| {
if (line.len == 0) continue;
var words = std.mem.split(u8, line, " ");
const left = try std.fmt.parseInt(u32, words.next() orelse return error.InvalidInput, 10);
const right = try std.fmt.parseInt(u32, words.next() orelse return error.InvalidInput, 10);
try lefts.append(left);
try rights.append(right);
}
return .{ .lefts = lefts, .rights = rights };
}
pub fn part1(_: std.mem.Allocator, input: Input) !u32 {
std.mem.sort(u32, input.lefts.items, {}, std.sort.asc(u32));
std.mem.sort(u32, input.rights.items, {}, std.sort.asc(u32));
var sum: u32 = 0;
for (input.lefts.items, input.rights.items) |l, r| {
sum += @max(l, r) - @min(l, r);
}
return sum;
}
pub fn part2(allocator: std.mem.Allocator, input: Input) !u32 {
var right_counts = std.AutoHashMap(u32, u16).init(allocator);
defer right_counts.deinit();
for (input.rights.items) |right| {
const entry = try right_counts.getOrPut(right);
if (entry.found_existing)
entry.value_ptr.* += 1
else
entry.value_ptr.* = 1;
}
var sum: u32 = 0;
for (input.lefts.items) |x| {
const count: u32 = @intCast(right_counts.get(x) orelse 0);
sum += x * count;
}
return sum;
}
|
