gistfile1.py

def missing(seq):
    num_missing = 2

    for i in xrange(num_missing):
        seq.append(None)

    for i in xrange(len(seq) - 2):
        if seq[i] == i:
            continue

        number = seq[i]
        while True:
            value_on_numbers_index = seq[number]
            if value_on_numbers_index == number \
                    or value_on_numbers_index is None:
                break
            seq[number] = number
            number = value_on_numbers_index

    res = []
    for i in xrange(1, len(seq)):
        if seq[i] != i:
            res.append(i)
            if len(res) == num_missing:
                break

    return res