Letter Case Permutation

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Leetcode

Medium

Strings

Backtracking

Recursion

Letter Case Permutation

Generate every string formed by toggling the letter cases in the input string while leaving digits unchanged.

Acceptance 0%

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Problem Statement

You are given a string s consisting of letters and digits.

Generate all possible strings that can be formed by independently changing each alphabetic character to either lowercase or uppercase. Digits must remain unchanged.

Return all distinct permutations in any order.

Notes

Each letter can be chosen in one of two cases.
Non-letter characters are not modified.
The same output string should not appear more than once.

Input Format

A single string s.
s contains only English letters and digits.

Output Format

Return a list of all valid case permutations of s in any order.

Constraints

1 <= s.length <= 12
s contains only letters and digits.
The number of alphabetic characters may be up to the length of the string.

Examples

Sample cases returned by the problem API.

Example 1

Input

s = "a1b2"

Output

["a1b2","a1B2","A1b2","A1B2"]

Explanation

The letters a and b can each be lowercase or uppercase, while digits stay unchanged.

Example 2

Input

s = "3z4"

Output

["3z4","3Z4"]

Explanation

Only z changes case; the digits 3 and 4 remain the same.

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