1const std = @import("std");
 2
 3pub fn pt1(input: []const u8) u64 {
 4    var counter: u64 = 0;
 5
 6    var lines = std.mem.splitScalar(u8, input, '\n');
 7
 8    while (lines.next()) |l| {
 9        if (l.len == 0) return counter;
10
11        var buff_line: [100]u8 = undefined;
12        parseLine(&buff_line, l);
13        counter += calcJolts(2, &buff_line);
14    }
15
16    return counter;
17}
18
19pub fn pt2(input: []const u8) u64 {
20    var counter: u64 = 0;
21
22    var lines = std.mem.splitScalar(u8, input, '\n');
23
24    while (lines.next()) |l| {
25        if (l.len == 0) return counter;
26
27        var buff_line: [100]u8 = undefined;
28        parseLine(&buff_line, l);
29        counter += calcJolts(12, &buff_line);
30    }
31
32    return counter;
33}
34
35fn parseLine(buff_line: []u8, line: []const u8) void {
36    for (0..line.len, line) |i, l| {
37        const d = l - '0';
38        buff_line[i] = d;
39    }
40}
41
42fn calcJolts(n: usize, js: []const u8) u64 {
43    var counter: u64 = 0;
44    var index: usize = 0;
45    for (0..n) |p| {
46        var inner_index = index;
47
48        // plus one to fix disparity between index (starts at 0) and size
49        const upper_bound = js.len - (n - p) + 1;
50        for (index..upper_bound) |i| {
51            if (js[inner_index] < js[i]) inner_index = i;
52        }
53
54        // the amounts of zeros is inverse to the position of p in relation to
55        // size. At p=0 we have the maximum numbers of zero n. At p=n-1, which
56        // p reached its maximum value, pow(10,0) which is 1 (thanks math for
57        // helping with the edge case).
58        const res = js[inner_index] * std.math.pow(u64, 10, n - p - 1);
59
60        counter += res;
61        index = inner_index + 1; // don't forget to advance index.
62    }
63
64    return counter;
65}
66
67test "Day 3 par 1" {
68    const res = pt1(@embedFile("./input/day3"));
69    try std.testing.expect(res == 17311);
70}
71
72test "Day 3 par 2" {
73    const res = pt2(@embedFile("./input/day3"));
74    try std.testing.expect(res == 171419245422055);
75}