Dear Monks,

Let's assume that I have a file called bit.txt :

bit.txt
=====================
110101010110111010101
100000000000000000001
101010101010101010101
110000000000000000011
110100000000000000000
11
[download]

And I want two things.

1) The regular expression that matches the lines containing an even number of 1s.
2) The regular expression that matches the lines containing an odd number of 1s.

My answer for these:

1) ^(0*10*10*)*$
2) ^(0*10*10*)*1(0*10*10*)*$
[download]

My question is: Are these the shortest possible RegExps for the job? Especially the second one? Can it be shorter?

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