MissingInteger Find the smallest positive integer that does not occur in a given sequence.

problem.md

Write a function:

fun solution(A: IntArray): Int

that, given an array A of N integers, returns the smallest positive integer (greater than 0) that does not occur in A.

For example, given A = [1, 3, 6, 4, 1, 2], the function should return 5.

Given A = [1, 2, 3], the function should return 4.

Given A = [−1, −3], the function should return 1.

Write an efficient algorithm for the following assumptions:

N is an integer within the range [1..100,000]; each element of array A is an integer within the range [−1,000,000..1,000,000].

solution.kt

fun solution(A: IntArray): Int {
    // write your code in Kotlin
    val maxNum = A.max()
    val N: Int = A.count()
    val set: MutableSet<Int> = HashSet()
    for (a in A) {
        if (a > 0) {
            set.add(a)
        }
    }
    for (i in 1..N + 1) {
        if (!set.contains(i)) {
            return i
        }
    }

    return (maxNum!! + 1)
}