Calculate Jaccard Similarity Score for Two String Lists

Scenario

During pair programming, the interviewer asks you to compare two lists of merchant tags and quantify their similarity.

Question

Implement a Python function that takes two lists of strings and returns their Jaccard similarity score.

Hints

Convert both lists to sets, then compute |A ∩ B| ÷ |A ∪ B|.

Calculate Jaccard Similarity Score for Two String Lists

During pair programming, the interviewer asks you to compare two lists of merchant tags and quantify their similarity.

Implement a function jaccardSimilarity(listA, listB) that takes two lists of strings and returns their Jaccard similarity score: the size of the intersection of the two sets of tags divided by the size of their union.

Formally, for sets A and B derived from the input lists:

Jaccard(A, B) = |A ∩ B| / |A ∪ B|

Duplicate tags within a single list should be treated as one (the lists are converted to sets). If both lists are empty (the union is empty), return 0.0 to avoid dividing by zero.

Example:

  listA = ["a", "b", "c"], listB = ["b", "c", "d"]
  Intersection = {"b", "c"} (size 2), Union = {"a", "b", "c", "d"} (size 4)
  Result = 2 / 4 = 0.5

Constraints

• 0 <= len(listA), len(listB) <= 10^5
• Each tag is a non-empty string of printable ASCII characters.
• Tags are case-sensitive ("Sale" and "sale" are distinct).
• Duplicate tags within the same list count once.
• If both lists are empty (union is empty), return 0.0.

Hints

1. Convert both lists to sets to discard duplicates and enable fast membership tests.
2. The intersection size is |A ∩ B| and the union size is |A ∪ B|; the score is their ratio.
3. Guard against division by zero: when the union is empty (both lists empty), return 0.0.