Advent of Code 2022 - Day 13: Distress Signal Solution

Part 1

Three cases:

• all is number
• all is array
• one is array

For each case, there are 3 possibilities of true, false, undetermined. But in the end there is only true, false. So keep in mind about that

Implementation

1const fs = require("fs")
2
3const readData = () => {
4  const data = fs
5    .readFileSync("./input", "utf-8")
6    .split(/\r?\n\r?\n/)
7    .map(line => line.split(/\r?\n/).map(part => JSON.parse(part)))
8
9  return data
10}
11
12const main = () => {
13  const pairs = readData()
14
15  const compare = ([left, right]) => {
16    if ([left, right].every(Number.isInteger)) {
17      if (left < right) return true
18      if (left > right) return false
19      return
20    }
21
22    if ([left, right].every(Array.isArray)) {
23      for (let i = 0; i < Math.min(left.length, right.length); i++) {
24        const res = compare([left[i], right[i]])
25        if (res != null) return res
26      }
27
28      return compare([left.length, right.length])
29    }
30
31    return compare([[left].flat(), [right].flat()])
32  }
33
34  const res = pairs.reduce(
35    (acc, el, index) => acc + (compare(el) ? index + 1 : 0),
36    0
37  )
38
39  console.log(res)
40}
41
42main()

Part 2

Flatten the pairs, add 2 dividers and sort the list of packets ascending

Implementation

1const fs = require("fs")
2
3const readData = () => {
4  const data = fs
5    .readFileSync("./input", "utf-8")
6    .split(/\r?\n\r?\n/)
7    .map(line => line.split(/\r?\n/).map(part => JSON.parse(part)))
8
9  return data
10}
11
12const main = () => {
13  const pairs = readData()
14
15  const compare = ([left, right]) => {
16    if ([left, right].every(Number.isInteger)) {
17      if (left < right) return true
18      if (left > right) return false
19      return
20    }
21
22    if ([left, right].every(Array.isArray)) {
23      for (let i = 0; i < Math.min(left.length, right.length); i++) {
24        const res = compare([left[i], right[i]])
25        if (res != null) return res
26      }
27
28      return compare([left.length, right.length])
29    }
30
31    return compare([[left].flat(), [right].flat()])
32  }
33
34  const dividers = [[[2]], [[6]]]
35
36  const res = [...pairs.flat(), ...dividers]
37    .sort((left, right) => compare([right, left]) - compare([left, right]))
38    .reduce(
39      (acc, el, index) => (dividers.includes(el) ? acc * (index + 1) : acc),
40      1
41    )
42
43  console.log(res)
44}
45
46main()

Trick

For the case that one of left or right is an array, instead of using ternary operator like

1Number.isInteger(left) ? compare([[left], right]) : compare([left, [right]])

we could make use of .flat

1compare([[left].flat(), [right].flat()])

References

Original problem

Array.prototype.flat()