Bug in algorithms/array/flatten.py, line 10

[TheoYuan]

Run the flatten(inputArr, outputArr=None) function in python3.5.
It seams ok when the test case is [2, 1, [3, [4, 5], 6], 7, [8]].
But when using [[3, [4, 5], 6], 7, [8]], function outputs [7, 8] not [3, 4, 5, 6, 7, 8].
That is because not None and not [] will be both True in line 10.
Take a = [[3, [4, 5], 6], 7, [8]] as example, first call flatten(a, None).
It will call flatten([3, [4, 5], 6], []). Run till line 10, not outputArr is True where outputArr is [].
Then outputArr will be assigned a new empty list. So it lose [3, 4, 5, 6] in recursive.
It is fine because the first element is single so not [2] is False in given test case.

Bug can fix in:
if outputArr is None:
or
def flatten(inputArr, outputArr=[]) and delete the if statement.

[goswami-rahul]

Nice catch @TheoYuan . if outputArr is None works fine 👍