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

Answer 1

Swift 3 - 100%

public func solution(_ A : inout [Int]) -> Int {
// write your code in Swift 3.0 (Linux)

var solution = 1
var hashSet = Set()

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

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

    return solution
}

Thanks to Marian's answer above.