Maximum Length of a Concatenated String with Unique Characters — LeetCode 1239 Python Solution

MediumBit ManipulationArrayStringBacktracking

Problem: #1239
Pattern: Backtracking
Reading time: 2 min
Source: leetcode.com

The problem

You are given an array of strings arr. A string s is formed by the concatenation of a subsequence of arr that has unique characters.

Example

Input: arr = ["un","iq","ue"]
Output: 4
Explanation: All the valid concatenations are:

Python solution

Python

class Solution:
    def maxLength(self, arr: List[str]) -> int:
        s = [0]
        for t in arr:
            x = 0
            for b in map(lambda c: ord(c) - 97, t):
                if x >> b & 1:
                    x = 0
                    break
                x |= 1 << b
            if x:
                s.extend((x | y) for y in s if (x & y) == 0)
        return max(x.bit_count() for x in s)

Complexity

Measure	Complexity
Time	O(2^n + L)
Space	O(2^n) auxiliary

Pattern: Backtracking

Build candidates one choice at a time and abandon a branch the moment it cannot work. LeetCode 1239. Maximum Length of a Concatenated String with Unique Characters is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Backtracking.

The backtracking guide has the Python template for the pattern and the 105 LeetCode problems that use it.

Frequently asked questions

How hard is LeetCode 1239. Maximum Length of a Concatenated String with Unique Characters?: LeetCode 1239. Maximum Length of a Concatenated String with Unique Characters is rated Medium on LeetCode.
What is the time complexity of LeetCode 1239. Maximum Length of a Concatenated String with Unique Characters?: The Python solution on this page runs in O(2^n + L).
What is the space complexity of LeetCode 1239. Maximum Length of a Concatenated String with Unique Characters?: The Python solution on this page uses O(2^n) auxiliary space.
What topics does LeetCode 1239. Maximum Length of a Concatenated String with Unique Characters cover?: LeetCode 1239. Maximum Length of a Concatenated String with Unique Characters is tagged Bit Manipulation, Array, String and Backtracking on LeetCode.