Day 11

day11part2.js

const fs = require('fs')
const input = fs.readFileSync('input.txt', 'utf-8').split(/\r\n/).map(line => line.split(''))

class Galaxy {
    row
    col
    rowInc = 0
    colInc = 0

    constructor(row, col) {
        this.row = row
        this.col = col
    }

    expandGalaxy() {
        this.row += this.rowInc
        this.col += this.colInc
        this.rowInc = 0
        this.colInc = 0
    }

    addRowInc() {
        this.rowInc += 999999
    }

    addColInc() {
        this.colInc += 999999
    }

    static distance(a, b) {
        const dx = Math.abs(a.col - b.col)
        const dy = Math.abs(a.row - b.row)
        return dx + dy
    }
}

//create galaxy array and find empty columns/rows
let galaxyArray = []
let emptyRowSpace = new Set(Array.from({ length: (input.length) }, (v, i) => i))
let emptyColSpace = new Set(Array.from({ length: (input[0].length) }, (v, i) => i))

for (let row = 0; row < input.length; row++) {
    for (let col = 0; col < input[0].length; col++) {
        if (input[row][col] == '#') {
            galaxyArray.push(new Galaxy(row, col))
            emptyRowSpace.delete(row)
            emptyColSpace.delete(col)
        }
    }
}



//for each empty col/row, mark glaxies for expansion as necessary...
emptyRowSpace.forEach(row => {
    galaxyArray.forEach(galaxy => {
        if (galaxy.row > row) {
            galaxy.addRowInc()
        }
    })
})
emptyColSpace.forEach(col => {
    galaxyArray.forEach(galaxy => {
        if (galaxy.col > col) {
            galaxy.addColInc()
        }
    })
})
//...then expand!
galaxyArray.forEach(galaxy => galaxy.expandGalaxy())

//find distance between all pairs of galaxies
let totalDistance = 0
for (let i = 0; i < galaxyArray.length - 1; i++) {
    for (let j = i + 1; j < galaxyArray.length; j++) {
        totalDistance += Galaxy.distance(galaxyArray[i], galaxyArray[j])
    }
}

console.log(totalDistance)