Question

1. Max Length of the String is 6.
2. The string should contain at most 2 digits
3. The string should contain at most 4 alphabets

So the following examples should match

abcd22

a1cd3d

11acde

a1c

1ad

Answer 1

What you want isn’t really possible in regular expressions because regular expressions can’t count, which would be required here. In fact, regular expressions seem to be able to count characters in direct sequence, e.g. in this case:

/x{2,3}/ # 2 or 3 ‘x’s

… but that’s actually not counting, because it’s just a shortcut for this expression:

/xxx?/

i.e. 2 x’s, followed by an optional third one.

Your expression, on the other hand, would have to keep track of two different counters over the whole automaton which represents the expression. That’s simply not possible in classical regular expressions (and still very hard using more modern incarnations of regular expressions which use pushdown automata to save states).