aoc21_5.js

import { accessSync, promises as fs } from 'fs';

(async()=>{
    const input = await fs.readFile("./interpretertests/aoc_21_5_input.txt", 'utf8')

    const drawing = (straight) => input.split('\n').reduce((acc, line) => {
        let [[x1,y1],[x2,y2]] = line.split(' -> ').map(x => x.split(',').map(x => parseInt(x)))
        
        if (straight && x1!=x2 && y1!=y2) return acc 

        if (Math.abs(x2-x1) > Math.abs(y2-y1)) {
            const yi = (y2-y1)/(x2-x1)
            const xi = x1>x2 ? -1 : 1
            let i = x1
            while (Math.abs(i-x2-xi)>0) {
                if (!acc.grid[i]) acc.grid[i] = []

                if (acc.grid[i][y1+(i-x1)*yi]) {
                    acc.grid[i][y1+(i-x1)*yi]++
                    if (acc.grid[i][y1+(i-x1)*yi]==2) acc.hits++
                } else
                acc.grid[i][y1+(i-x1)*yi] = 1

                i+=xi
            }
        } else {
            const xi = (x2-x1)/(y2-y1)
            const yi = y1>y2 ? -1 : 1
            let i = y1  
            while (Math.abs(i-y2-yi)>0) {

                if (!acc.grid[x1+(i-y1)*xi]) acc.grid[x1+(i-y1)*xi] = []

                if (acc.grid[x1+(i-y1)*xi][i]) {
                    acc.grid[x1+(i-y1)*xi][i]++
                    if (acc.grid[x1+(i-y1)*xi][i]==2) acc.hits++
                } else
                acc.grid[x1+(i-y1)*xi][i] = 1

                i+=yi
            }
        }

        return acc
    }, {grid:[], hits: 0})

    //console.table(drawing2.grid)
    console.log(drawing(true).hits)
    console.log(drawing(false).hits)
})();