advent of code 2024 chiri solutions day 2

part 1.js

input.split(/\s*\n\s*/g)
    .map((report, i, a, 
          levels = report.split(/\s+/g).map(level => +level), 
          dirs = new Set(levels.map((v, i) => i === 0 ? 10 : Math.sign(v - levels[i - 1]))),
          dists = levels.map((v, i) => i === 0 ? 1 : Math.abs(v - (levels[i - 1] ?? 0))),
         ) => ({ 
        levels,
        dirs,
        dists,
        safe: dirs.size === 2 && dists.every(dist => dist >= 1 && dist <= 3),
    })).filter(report => report.safe)

part 2.js

function count(arr, filter) { return arr.reduce((c, v) => c + +!!filter(v), 0) }

input.split(/\s*\n\s*/g)
    .filter(report => isReportSafe(report.split(/\s+/g).map(level => +level)))

function isReportSafe(levels, recursive = false) {
    const dirs = levels.map((v, i) => i === 0 ? 0 : Math.sign(v - levels[i - 1]))
    dirs.shift()
    const dists = levels.map((v, i) => i === 0 ? 0 : Math.abs(v - (levels[i - 1] ?? 0)))
    dists.shift()

    const invalidDistsCount = count(dists, dist => dist < 1 || dist > 3)
    if (invalidDistsCount > 2)
        return false

    if (!invalidDistsCount && dirs[0] !== 0 && new Set(dirs).size === 1)
        return true

    if (recursive)
        return false // if the above checks failed this tweak to the report is unsafe

    const noDirs = count(dirs, dir => dir === 0)
    if (noDirs > 1)
       return false // 0 more than once is always invalid
    
    const negDirs = count(dirs, dir => dir === -1)
    const posDirs = count(dirs, dir => dir === 1)

    if (negDirs > 1 && posDirs > 1)
        return false // both directions each more than once is always invalid

    return levels.some((v, i) => isReportSafe(levels.toSpliced(i, 1), true))
}