Day 2: Red-Nosed Reports

Megathread guidelines

  • Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
  • You can send code in code blocks by using three backticks, the code, and then three backticks or use something such as https://blocks.programming.dev/ if you prefer sending it through a URL

FAQ

  • proved_unglue@programming.dev
    link
    fedilink
    arrow-up
    1
    ·
    2 days ago

    Kotlin

    A bit late to the party, but here you go.

    import kotlin.math.abs
    
    fun part1(input: String): Int {
        return solve(input, ::isSafe)
    }
    
    fun part2(input: String): Int {
        return solve(input, ::isDampSafe)
    }
    
    private fun solve(input: String, condition: (List<Int>) -> Boolean): Int {
        var safeCount = 0
        input.lines().forEach { line ->
            if (line.isNotBlank()) {
                val nums = line.split("\\s+".toRegex()).map { it.toInt() }
                safeCount += if (condition(nums)) 1 else 0
            }
        }
        return safeCount
    }
    
    private fun isSafe(list: List<Int>): Boolean {
        val safeDiffs = setOf(1, 2, 3)
        var incCount = 0
        var decCount = 0
        for (idx in 0..<list.lastIndex) {
            if (!safeDiffs.contains(abs(list[idx] - list[idx + 1]))) {
                return false
            }
            if (list[idx] <= list[idx + 1]) incCount++
            if (list[idx] >= list[idx + 1]) decCount++
        }
        return incCount == 0 || decCount == 0
    }
    
    private fun isDampSafe(list: List<Int>): Boolean {
        if (isSafe(list)) {
            return true
        } else {
            for (idx in 0..list.lastIndex) {
                val shortened = list.toMutableList()
                shortened.removeAt(idx)
                if (isSafe(shortened)) {
                    return true
                }
            }
        }
        return false
    }