Max Total Characters by Selecting Words with Unique Letters

Problem Given an array of strings words, choose a subset and concatenate them in any order. Constraint: Across the entire concatenated string, no letter may appear more than once (letters cannot repeat across chosen words). Return the maximum possible total length of such a concatenation. Input First line: integer k Next k lines: one word per line Output An integer: the maximum length. Typical Constraints 1 <= k <= 16 (larger needs bitmasking/pruning) words contain only lowercase a-z Example Input: 4 un iq ue aa Output: 4 Explanation: pick un + iq => length 4; aa is invalid due to repeated letters within the word. Example Input 4 un iq ue aa Output 4