Compute Jaccard similarity between two strings

## Jaccard Similarity of Two Strings Given two strings `a` and `b`, compute their **Jaccard similarity** based on token sets. ### Tokenization rules - Convert to lowercase. - Split on any non-alphabetic character (e.g., spaces, punctuation). - Discard empty tokens. - Treat each string as a **set** of unique tokens (ignore duplicates). ### Jaccard similarity Let `A` be the token set from `a` and `B` from `b`. \[ J(A,B) = \frac{|A \cap B|}{|A \cup B|} \] ### Output Return the similarity as a floating-point number. ### Edge cases - If both sets are empty, define similarity as `1.0`. ### Example - `a = "I like coffee, coffee"` - `b = "coffee is great"` - `A = {i, like, coffee}` - `B = {coffee, is, great}` - Intersection size = 1, Union size = 5 → similarity = `0.2`