You are given an array `words` of lowercase English strings. Choose a subset of words such that: - each chosen word contains no repeated letter within itself, and - no letter appears in more than one chosen word. The score of a subset is the number of distinct letters covered by all chosen words combined. Return the maximum possible score. If multiple subsets achieve the same score, any one of them is acceptable. Example: - Input: the 12 month abbreviations such as `jan`, `feb`, ..., `dec` - The subset `{jan, feb, may}` is **invalid** because the letter `a` appears in both `jan` and `may`. - A valid answer must use words whose character sets are pairwise disjoint. Design an efficient algorithm. You may assume all characters come from the 26 lowercase English letters.