Complexity of Regex substitution

Question

I didn\'t get the answer to this anywhere. What is the runtime complexity of a Regex match and substitution?

Edit: I work in python. But would like to know in genera

Answer 1

You can trade space for speed by building a nondeterministic finite automaton instead of a DFA. This can be traversed in linear time. Of course, in the worst case this could need O(2^m) space. I'd expect the tradeoff to be worth it.