# Advent of Code 2021 - Day 13

## Day 13a

``````const parseDots = (input: string) =>
ranks(ints(input), 2).map(([x, y]) => ({x, y} as Point))

const parseFolds = (input: string) =>
Array.from(input.matchAll(/([xy])=(\d+)/g)).map(
([_, xy, n]) => ({x: 0, y: 0, [xy]: n} as Point),
)

const parse = (input: string) =>
R.zipWith([parseDots, parseFolds], paras(input), (f, s) => f(s))

const fold = (dots: Point[], f: Point) =>
R.pipe(
dots.map(({x, y}) => ({
x: f.x && x > f.x ? x - (x - f.x) * 2 : x,
y: f.y && y > f.y ? y - (y - f.y) * 2 : y,
})),
R.uniqBy(({x, y}) => `\${x},\${y}`),
)

export const d13a = ({input = inputs.d13}: {input: string}) => {
const [dots, folds] = parse(input)
return fold(dots, folds[0]).length
}``````

Example:

Mine:

## Day 13b

``````const draw = (dots: Point[]) => {
const ds = dots.reduce((o, {x, y}) => {
o[y] = o[y] || {}
o[y][x] = true
return o
}, {})
const [[minx, maxx], [miny, maxy]] = ['x', 'y']
.map(a => dots.map(p => p[a]))
.map(ds => juxt(ds, [min, max]))
return (
'\n' +
R.range(miny, maxy + 1)
.map(y =>
R.range(minx, maxx + 1)
.map(x => (ds[y]?.[x] ? '#' : '.'))
.join(''),
)
.join('\n')
)
}

export const d13b = ({input = inputs.d13}: {input: string}) => {
const [dots, folds] = parse(input)
return draw(folds.reduce(fold, dots))
}``````

Example:

Mine: