Missing number.kt

fun missingNumber(input: IntArray): Int {
    val n = input.size + 1
    val expectedSum = (n * (n + 1)) / 2
    val actualSum = input.sum()
    return expectedSum - actualSum
}


fun missingNumber(input: IntArray): Int {
   if(input.isEmpty() || input.count() == 1) {
       return 1
   }
   val expectedArray = IntArray(input.count() + 1) { it + 1 }
   return expectedArray.subtract(input.asIterable()).toList().firstOrNull() ?: 1
}