# 1239. Maximum Length of a Concatenated String with Unique Characters
Given an array of strings arr. String s is a concatenation of a sub-sequence of arr which have unique characters.
Return the maximum possible length of s.
Example 1:
Input: arr = ["un","iq","ue"]
Output: 4
Explanation: All possible concatenations are "","un","iq","ue","uniq" and "ique".
Maximum length is 4.
Example 2:
Input: arr = ["cha","r","act","ers"]
Output: 6
Explanation: Possible solutions are "chaers" and "acters".
Example 3:
Input: arr = ["abcdefghijklmnopqrstuvwxyz"]
Output: 26
# Solution
Approach 1: enumerate all combinations.
# Code (Python)
Approach 1:
def maxLength(self, words: List[str]) -> int:
# idea: enumerate all combinations, but append those to a long, long list (see Combinations problems)
# can also use bitmaps: bitmap_so_far | ord(letter) - ord('a')
concated = [set()]
for word in words:
# ignore words with dup chars in itself
if len(set(word)) != len(word):
continue
# trick: use a copy of concated to do the iteration while appending to it
for concat in (_ for _ in concated):
if concat & set(word):
continue
concated.append(concat | set(word))
return max(map(len, concated))
# Code (C++)
Approach 1:
Approach 2: