https://www.hackerrank.com/challenges/picking-numbers/problem

HackerRank_PickingNumbers.kt

fun pickingNumbers(a: Array<Int>): Int {
    var ret = Int.MIN_VALUE
    val map = hashMapOf<Int, Int>()
    a.forEach { i ->
        map[i] = a.filter { it == i }.size
    }

    for (i in map.keys) {
        val value = map[i]!!.plus(map.getOrDefault(i - 1, 0))
        if (value > ret) {
            ret = value
        }
    }

    return ret
}

fun main(args: Array<String>) {
    val n = readLine()!!.trim().toInt()

    val a = readLine()!!.trimEnd().split(" ").map { it.toInt() }.toTypedArray()

    val result = pickingNumbers(a)

    println(result)
}