Maximize unique characters from a word list

## Maximize Unique Characters From a Word List You are given a list of strings `words`. You may select **any subset** of these strings (each string used at most once) and concatenate them in any order. A concatenation is **valid** if **no character appears more than once** in the final concatenated string. ### Task Return the **maximum possible length** of a valid concatenation. ### Input/Output - Input: `words: List[str]` - Output: `int` = maximum valid concatenation length ### Constraints (reasonable interview assumptions) - `1 <= len(words) <= 20` - Each word contains only lowercase English letters `a-z` - `1 <= len(word) <= 26` ### Examples - `words = ["un","iq","ue"]` → `4` ("uniq" or "ique") - `words = ["aa","bc"]` → `2` (skip "aa", take "bc")