Letter Case Permutation

medium

stringTime: O(n * 2^k) where k = number of letters in sSpace: O(n * 2^k) for storing all permutationsFrequency: 2

Given a string s, you can transform every letter individually to be lowercase or uppercase to create another string.

Return a list of all possible strings we could create. Return the output in any order.

Constraints: 1 <= s.length <= 12. s consists of lowercase English letters, uppercase English letters, and digits.

Example 1:

Input: s = "a1b2"
Output: ["a1b2","a1B2","A1b2","A1B2"]

Example 2:

Input: s = "3z4"
Output: ["3z4","3Z4"]

recursion

Shortcuts

Interview tips

→Aim for O(n * 2^k) where k = number of letters in s time and O(n * 2^k) for storing all permutations space.
→Walk through your approach with a small example first.
→Handle edge cases: empty input, single element, overflow.
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