coinChange.kt

// coin change kata

fun largestCoin(coins: IntArray, amount: Int): Int? =
    try {
        coins.first { coin -> coin <= amount }
    } catch (_: NoSuchElementException) {
        null
    }

fun coinChange(coins: IntArray, amount: Int): Int {
    val coinsSorted = coins.sortedArrayDescending()
    
    tailrec fun recur(count: Int = 0, amount: Int): Int {
        return if (amount == 0) {
            count
        } else {
            val coin = largestCoin(coinsSorted, amount) ?: return -1

            recur(count + 1, amount - coin)
        }
    }

    return recur(amount = amount)
}