class Solution:
    def maxLength(self, arr: List[str]) -> int:
        # Remove words with duplicate letters
        arr = [s for s in arr if len(s) == len(set(s))]

        def to_letters_bitset(s: str) -> int:
            ret = 0
            for c in s:
                ret |= 1 << (ord(c) - ord('a'))
            return ret
        letters = [to_letters_bitset(s) for s in arr]

        ans = 0
        comb = 1
        MAX_COMB = 2 ** len(arr)
        while comb < MAX_COMB:
            comb_inc = 1

            cur_letters = 0
            cur_len = 0
            for i in range(len(arr) - 1, -1, -1):
                cur_bit = 2 ** i
                if (cur_bit & comb) == 0:
                    continue
                if (cur_letters & letters[i]) != 0:
                    comb -= comb & (cur_bit * 2 - 1)
                    comb_inc = cur_bit * 2
                    break
                cur_letters |= letters[i]
                cur_len += len(arr[i])
            # We don't have to care if comb is valid as used_letters and
            # cur_len are only increased when we have a valid prefix of comb
            ans = max(ans, cur_len)
            comb += comb_inc
        return ans