+ "ers") and "acters" ("act" + "ers").

Example 3:

Input: arr = ["abcdefghijklmnopqrstuvwxyz"]
Output: 26
Explanation: The only string in arr has all 26 characters.

Solution

Method 1 - Backtracking

Here is the approach:

Backtracking: We will use backtracking to explore all possible subsequences of the given array.
Unique Characters: For each subsequence, we will check if the concatenated string has all unique characters.
Max Length: We will keep track of the maximum length of such valid strings.

Code

[{"language":"Java","code":"class Solution {\n    public int maxLength(List<String> arr) {\n        return helper(arr, 0, \"\");\n    }\n\n    private int helper(List<String> arr, int start, String current) {\n        if (!isUnique(current)) return 0;\n        int ans = current.length();\n        for (int i = start; i < arr.size(); i++) {\n            ans = Math.max(ans, helper(arr, i + 1, current + arr.get(i)));\n        }\n        return ans;\n    }\n\n    private boolean isUnique(String s) {\n        Set<Character> set = new HashSet<>();\n        for (char c : s.toCharArray()) {\n            if (set.contains(c)) return false;\n            set.add(c);\n        }\n        return true;\n    }\n}","lang":"java","html":"<pre class=\"shiki shiki-themes github-light github-dark\" style=\"background-color:#fff;--shiki-dark-bg:#24292e;color:#24292e;--shiki-dark:#e1e4e8\" tabindex=\"0\"><code><span class=\"line\"><span style=\"color:#D73A49;--shiki-dark:#F97583\">class</span><span style=\"color:#6F42C1;--shiki-dark:#B392F0\"> Solution</span><span s

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