Introduction

In this blog post, we will explore how to solve the LeetCode problem "784" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like Chatmagic, we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

Problem Statement

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. Example 1: Input: s = "a1b2" Output: ["a1b2","a1B2","A1b2","A1B2"] Example 2: Input: s = "3z4" Output: ["3z4","3Z4"] Constraints: 1 <= s.length <= 12 s consists of lowercase English letters, uppercase English letters, and digits.

Explanation

• Backtracking: The core idea is to use backtracking. For each character in the input string, we explore the possibility of either converting it to lowercase or uppercase (if it's a letter) or leaving it as is (if it's a digit).

• Recursive Exploration: We recursively build up possible strings. At each step, we append either the lowercase or uppercase version (or the original character if it's a digit) to the current string being built, and then recursively call the function to process the remaining part of the input string.

• Base Case: The recursion stops when we have processed all the characters in the input string. At this point, we add the fully constructed string to the list of results.

• Runtime Complexity: O(2^N), where N is the number of letters in the string. Storage Complexity: O(2^N) to store the results.

Code

    def letterCasePermutation(s: str) -> list[str]:
    """
    Generates all possible strings by transforming each letter in the input string
    to be lowercase or uppercase.

    Args:
        s: The input string.

    Returns:
        A list of all possible strings.
    """
    result = []

    def backtrack(index: int, current_string: str):
        """
        Recursive helper function to explore all possible letter case permutations.

        Args:
            index: The current index being processed in the input string.
            current_string: The string built so far.
        """
        if index == len(s):
            result.append(current_string)
            return

        char = s[index]

        if char.isalpha():
            backtrack(index + 1, current_string + char.lower())
            backtrack(index + 1, current_string + char.upper())
        else:
            backtrack(index + 1, current_string + char)

    backtrack(0, "")
    return result