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

Answer 1

    static int spn(int[] array)
    {
        int returnValue = 1;
        int currentCandidate = 2147483647;

        foreach (int item in array)
        {
            if (item > 0)
            {
                if (item < currentCandidate)
                {
                    currentCandidate = item;
                }
                if (item <= returnValue)
                {
                    returnValue++;
                } 
            }
        }

        return returnValue;
    }