Advent of Code 2022 - Day 11: Monkey in the Middle Solution

Part 1

Purely adhoc

Implementation

1const fs = require("fs")
2
3const readData = () => {
4  const data = fs
5    .readFileSync("./input", "utf-8")
6    .split(/\r?\n/)
7    .filter(Boolean)
8
9  const monkeys = {}
10
11  for (let i = 0; i < data.length; i += 6) {
12    const monkeyNumber = i / 6
13    monkeys[monkeyNumber] = {}
14    monkeys[monkeyNumber].items = data[i + 1]
15      .replace("Starting items: ", "")
16      .trim()
17      .replace(/,/g, "")
18      .split(" ")
19      .map(Number)
20
21    monkeys[monkeyNumber].op = (() => {
22      const [operator, operand2] = data[i + 2]
23        .replace("Operation: new = old ", "")
24        .trim()
25        .split(" ")
26
27      const isMirror = operand2 === "old"
28
29      return {
30        "+": (operand, isMirror) => x => x + (isMirror ? x : operand),
31        "-": (operand, isMirror) => x => x - (isMirror ? x : operand),
32        "*": (operand, isMirror) => x => x * (isMirror ? x : operand),
33        "/": (operand, isMirror) => x => x / (isMirror ? x : operand),
34      }[operator](+operand2, isMirror)
35    })()
36
37    monkeys[monkeyNumber].test = (() => {
38      const divisibleBy = +data[i + 3].replace("Test: divisible by ", "").trim()
39      const destMonkeyIfTrue = +data[i + 4]
40        .replace("If true: throw to monkey ", "")
41        .trim()
42      const destMonkeyIfFalse = +data[i + 5]
43        .replace("If false: throw to monkey ", "")
44        .trim()
45
46      return {
47        fn: x => x % divisibleBy === 0,
48        destMonkeys: [destMonkeyIfFalse, destMonkeyIfTrue],
49      }
50    })()
51
52    monkeys[monkeyNumber].itemsInspectedTimes = 0
53  }
54
55  return Object.values(monkeys)
56}
57
58const main = () => {
59  const monkeys = readData()
60
61  let numberOfRounds = 20
62
63  while (numberOfRounds--) {
64    for (const [monkeyNo, monkey] of Object.entries(monkeys)) {
65      for (let itemIndex = 0; itemIndex < monkey.items.length; itemIndex++) {
66        const item = monkey.items[itemIndex]
67        let worryLevel = monkey.op(item)
68        worryLevel = Math.floor(worryLevel / 3)
69        const destMonkey = monkey.test.destMonkeys[+monkey.test.fn(worryLevel)]
70        monkeys[monkeyNo].items.splice(itemIndex, 1)
71        itemIndex--
72        monkeys[monkeyNo].itemsInspectedTimes++
73        monkeys[destMonkey].items.push(worryLevel)
74      }
75    }
76  }
77
78  const res = monkeys
79    .map(({ itemsInspectedTimes }) => itemsInspectedTimes)
80    .sort((a, b) => b - a)
81    .slice(0, 2)
82    .reduce((acc, el) => acc * el, 1)
83
84  console.log(res)
85}
86
87main()

Part 2

Use modulo operation to avoid number explosion (BigInt)

I'm suck at math so I borrowed the solution and leave some others' comments as references below:

• Comment 1
• Comment 2

Implementation

1const fs = require("fs")
2
3const readData = () => {
4  const data = fs
5    .readFileSync("./input", "utf-8")
6    .split(/\r?\n/)
7    .filter(Boolean)
8
9  const monkeys = {}
10
11  for (let i = 0; i < data.length; i += 6) {
12    const monkeyNumber = i / 6
13    monkeys[monkeyNumber] = {}
14    monkeys[monkeyNumber].items = data[i + 1]
15      .replace("Starting items: ", "")
16      .trim()
17      .replace(/,/g, "")
18      .split(" ")
19      .map(Number)
20
21    monkeys[monkeyNumber].op = (() => {
22      const [operator, operand2] = data[i + 2]
23        .replace("Operation: new = old ", "")
24        .trim()
25        .split(" ")
26
27      const isMirror = operand2 === "old"
28
29      return {
30        "+": (operand, isMirror) => x => x + (isMirror ? x : operand),
31        "-": (operand, isMirror) => x => x - (isMirror ? x : operand),
32        "*": (operand, isMirror) => x => x * (isMirror ? x : operand),
33        "/": (operand, isMirror) => x => x / (isMirror ? x : operand),
34      }[operator](+operand2, isMirror)
35    })()
36
37    monkeys[monkeyNumber].test = (() => {
38      const divisibleBy = +data[i + 3].replace("Test: divisible by ", "").trim()
39      const destMonkeyIfTrue = +data[i + 4]
40        .replace("If true: throw to monkey ", "")
41        .trim()
42      const destMonkeyIfFalse = +data[i + 5]
43        .replace("If false: throw to monkey ", "")
44        .trim()
45
46      return {
47        divisibleBy,
48        fn: x => x % divisibleBy === 0,
49        destMonkeys: [destMonkeyIfFalse, destMonkeyIfTrue],
50      }
51    })()
52
53    monkeys[monkeyNumber].itemsInspectedTimes = 0
54  }
55
56  return Object.values(monkeys)
57}
58
59const main = () => {
60  const monkeys = readData()
61
62  let numberOfRounds = 10000
63
64  const modulo = monkeys
65    .map(({ test: { divisibleBy } }) => divisibleBy)
66    .reduce((acc, el) => acc * el, 1)
67
68  while (numberOfRounds--) {
69    for (const [monkeyNo, monkey] of Object.entries(monkeys)) {
70      monkey.itemsInspectedTimes += monkey.items.length
71      for (let itemIndex = 0; itemIndex < monkey.items.length; itemIndex++) {
72        const item = monkey.items[itemIndex]
73        let worryLevel = monkey.op(item)
74        worryLevel = worryLevel % modulo
75        const destMonkey = monkey.test.destMonkeys[+monkey.test.fn(worryLevel)]
76        monkeys[monkeyNo].items.splice(itemIndex, 1)
77        itemIndex--
78        monkeys[destMonkey].items.push(worryLevel)
79      }
80    }
81  }
82
83  const res = monkeys
84    .map(({ itemsInspectedTimes }) => itemsInspectedTimes)
85    .sort((a, b) => b - a)
86    .slice(0, 2)
87    .reduce((acc, el) => acc * el, 1)
88
89  console.log(res)
90}
91
92main()

References

Original problem