Missing integer variation - O(n) solution needed [closed]

Answer 1

This is my solution is Swift 4

public func solution(_ A: inout [Int]) -> Int {

    var minNum = 1
    var hashSet = Set()

    for int in A {
        if int > 0 {
            hashSet.insert(int)
        }
    }

    while hashSet.contains(minNum) {
        minNum += 1
    }

    return minNum

}

var array = [1,3,6]

solution(&array)

// Answer: 2