Advent of Code 2020 Day 9

aoc202day09.kt

    fun part1(): Long {
        val prevFive = ArrayDeque<Long>()
        prevFive.addAll(input.subList(0, 25))
        for (i in 25 until input.size) {
            val elem = input[i]
            if (!prevFive.any { prevFive.contains(elem - it) }) return elem
            prevFive.removeFirst()
            prevFive.addLast(elem)
        }
        return -1
    }

    fun part2(): Long {
        val target = part1()
        for (i in input.indices) {
            for (j in i + 1 until input.size) {
                val range = input.subList(i, j+1)
                if (range.sum() == target) return range.minOrNull()!! + range.maxOrNull()!!
            }
        }
        return -1
    }