Introduction

In this blog post, we will explore how to solve the LeetCode problem "917" 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, reverse the string according to the following rules: All the characters that are not English letters remain in the same position. All the English letters (lowercase or uppercase) should be reversed. Return s after reversing it. Example 1: Input: s = "ab-cd" Output: "dc-ba" Example 2: Input: s = "a-bC-dEf-ghIj" Output: "j-Ih-gfE-dCba" Example 3: Input: s = "Test1ng-Leet=code-Q!" Output: "Qedo1ct-eeLg=ntse-T!" Constraints: 1 <= s.length <= 100 s consists of characters with ASCII values in the range [33, 122]. s does not contain '\"' or '\'.

Explanation

Here's a solution to the string reversal problem, focusing on efficiency and clarity.

• Two-Pointer Approach: Use two pointers, left and right, initialized to the start and end of the string, respectively.
• Conditional Swapping: Move the pointers inwards, skipping non-letter characters. When both pointers point to letters, swap them.

• In-place Modification: Modify the string in-place to avoid extra space usage.

• Time Complexity: O(n), where n is the length of the string. Space Complexity: O(1) (in-place modification).

Code

    def reverse_only_letters(s: str) -> str:
    """
    Reverses the English letters in a string while keeping other characters in place.
    """
    s_list = list(s)  # Convert string to list for in-place modification
    left, right = 0, len(s) - 1

    while left < right:
        if not s_list[left].isalpha():
            left += 1
        elif not s_list[right].isalpha():
            right -= 1
        else:
            s_list[left], s_list[right] = s_list[right], s_list[left]
            left += 1
            right -= 1

    return "".join(s_list)  # Convert list back to string