day10.test.ts

/* === TYPES === */
type Diffs = Record<1 | 3, number>;

/* === PREPARE INPUT === */
export const prepareInput = ([input]: TemplateStringsArray) =>
  input.split("\n").map(Number);

/* === UTILS === */
const numCompare = (a: number, b: number) => a - b;
const last = <T>(xs: T[]): T => xs[xs.length - 1];
const empty = (): Diffs => ({ 1: 0, 3: 0 });
const toDiff = (xs: number[]): (1 | 3)[] =>
  xs.map((x, i) => (x - (xs[i - 1] || 0)) as 1 | 3);
const product = (a: number, b: number) => a * b;

// Ways of passing x ones in a row
const COMBINATIONS = [1, 1, 2, 4, 7];
const toCombinations = (x: number) => COMBINATIONS[x];

const countOccurences = (xs: (1 | 3)[]) =>
  xs.reduce((diffs, x) => {
    diffs[x] = diffs[x] + 1;
    return diffs;
  }, empty());

/* === IMPLEMENTATION === */
const joltageDiff = (adapters: number[]): Diffs => {
  const sorted = adapters.sort(numCompare);

  const withDevice = [...sorted, last(sorted) + 3];

  return countOccurences(toDiff(withDevice));
};

const countCombinations = (adapters: number[]): number =>
  toDiff(adapters)
    .join("")
    .split("3") // get rows of ones in between 3s
    .filter(Boolean)
    .map((group) => group.length)
    .map(toCombinations)
    .reduce(product, 1);

/* === TESTS === */

test("Day 10a - test", () => {
  const diffs = joltageDiff(testInput);

  expect(diffs[1] * diffs[3]).toBe(220);
});

test("Day 10a - prod", () => {
  const diffs = joltageDiff(prodInput);

  expect(diffs[1] * diffs[3]).toBe(1836);
});

test("Day 10b - test", () => {
  const result = countCombinations(testInput);

  expect(result).toBe(19208);
});

test("Day 10b - prod", () => {
  const result = countCombinations(prodInput);

  expect(result).toBe(43406276662336);
});

/* === INPUTS === */

const testInput = prepareInput`28
33
18
42
31
14
46
20
48
47
24
23
49
45
19
38
39
11
1
32
25
35
8
17
7
9
4
2
34
10
3`;

const prodInput = prepareInput`71
30
134
33
51
115
122
38
61
103
21
12
44
129
29
89
54
83
96
91
133
102
99
52
144
82
22
68
7
15
93
125
14
92
1
146
67
132
114
59
72
107
34
119
136
60
20
53
8
46
55
26
126
77
65
78
13
108
142
27
75
110
90
35
143
86
116
79
48
113
101
2
123
58
19
76
16
66
135
64
28
9
6
100
124
47
109
23
139
145
5
45
106
41`;