def least_common(column):
    """
    >>> least_common(["0", "0", "1"])
    '1'
    >>> least_common(["1", "1", "0", "0", "1"])
    '0'
    """
    occurs = {}
    for bit in column:
        occurs[bit] = occurs.get(bit, 0) + 1
    if occurs["0"] == occurs["1"]:
        return "0"
    return min(occurs, key=lambda v: occurs[v])