day6.js

//----------------------------------------------------
// main script
import fs = require("fs")
import _ = require("lodash")
import parse = require("./parse")
import decode = require("./decode")

const input = fs.readFileSync("./input.txt", "utf8")
const columns = parse(input)
const decoded = decode(columns)

console.log(`Part A: decoded word is ${decoded.mostFrequent}`)
console.log(`Part B: decoded word is ${decoded.leastFrequent}`)








//--------------------------------------
// parse.ts
"use strict"

import _ = require("lodash")

interface Input {
  columns: string[][]
}

function getColumn(lines: string[], column: number): string[] {
  return _(lines)
    .map(x => x.charAt(column))
    .value()
}

function parse(input: string): Input {
  const numberOfColumns = 8
  const lines = _(input.split("\n"))
    .map(x => x.trim())
    .filter(x => x !== "")
    .value()

  const columns = _(_.range(0, numberOfColumns))
    .map(x => getColumn(lines, x))
    .value()
  return { columns }
}

export = parse






//--------------------------------------
//decode.ts
import _ = require("lodash")

interface Input {
  columns: string[][]
}

interface ColumnResult {
  mostFrequent: string,
  leastFrequent: string
}

interface DecodeResult {
  mostFrequent: string,
  leastFrequent: string
}

function getMostAndLeastFrequentLetters(column: string[]): ColumnResult {
  const groups = _(column)
    .groupBy(x => x)
    .value()

  const letters = []
  _.forOwn(groups, (value, key) => {
    letters.push({
      letter: key,
      occurrences: value.length
    })
  })

  const mostFrequent = _(letters)
    .sortBy(x => x.occurrences)
    .map(x => x.letter)
    .last()
  const leastFrequent = _(letters)
    .sortBy(x => x.occurrences)
    .map(x => x.letter)
    .first()

  return {
    mostFrequent,
    leastFrequent
  }
}

function decode(input: Input): DecodeResult {
  const lettersArray = _(input.columns)
    .map(column => getMostAndLeastFrequentLetters(column))
    .value()

  const mostFrequent = _(lettersArray)
    .map(x => x.mostFrequent )
    .join("")
  const leastFrequent = _(lettersArray)
    .map(x => x.leastFrequent )
    .join("")

  return {
    mostFrequent,
    leastFrequent
  }
}

export = decode