_ = @import("day10.zig");

    const day10 = @import("day10.zig");

const days = 9;

const days = 10;

const std = @import("std");
const PATH = "../input/day10.txt";
const Str = []const u8;
pub fn first(allocator: ?std.mem.Allocator) anyerror!usize {
    const adapters = try parseInput(allocator.?, @embedFile(PATH));
    defer allocator.?.free(adapters);
    var one: usize = 0;
    var three: usize = 0;
    var idx: usize = 1;
    while (idx < adapters.len) : (idx += 1) {
        switch (adapters[idx] - adapters[idx - 1]) {
            1 => one += 1,
            3 => three += 1,
            else => unreachable,
        }
    }
    return one * three;
}
pub fn second(allocator: ?std.mem.Allocator) anyerror!usize {
    const adapters = try parseInput(allocator.?, @embedFile(PATH));
    defer allocator.?.free(adapters);
    var sum: usize = 1;
    var count: u3 = 0;
    var idx: usize = 1;
    while (idx < adapters.len) : (idx += 1) {
        const diff = adapters[idx] - adapters[idx - 1];
        if (diff == 1) {
            count += 1;
        } else {
            switch (count) {
                4 => sum *= 7, // ways to arrange 4 items
                3 => sum *= 4,
                2 => sum *= 2,
                1, 0 => {},
                else => unreachable,
            }
            count = 0;
        }
    }
    return sum;
}
fn parseInput(allocator: std.mem.Allocator, input: Str) ![]usize {
    var ret = std.ArrayList(usize).init(allocator);
    var lines = std.mem.tokenize(u8, input, "\n");
    while (lines.next()) |line| {
        try ret.append(try std.fmt.parseUnsigned(usize, line, 0));
    }
    try ret.append(0); // add charging outlet
    std.sort.sort(usize, ret.items, {}, comptime std.sort.asc(usize));
    try ret.append(ret.items[ret.items.len - 1] + 3); // add built-in adapter
    return ret.toOwnedSlice();
}
test "day10a" {
    try std.testing.expectEqual(@as(usize, 2482), try first(std.testing.allocator));
}
test "day10b" {
    try std.testing.expectEqual(@as(usize, 96717311574016), try second(std.testing.allocator));
}

66
7
73
162
62
165
157
158
137
125
138
59
36
40
94
95
13
35
136
96
156
155
24
84
42
171
142
3
104
149
83
129
19
122
68
103
74
118
20
110
54
127
88
31
135
26
126
2
51
91
16
65
128
119
67
48
111
29
49
12
132
17
41
166
75
146
50
30
1
164
112
34
18
72
97
145
11
117
58
78
152
90
172
163
89
107
45
37
79
159
141
105
10
115
69
170
25
100
80
4
85
169
106
57
116
23