Introduction

In this blog post, we will explore how to solve the LeetCode problem "1542" 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

You are given a string s. An awesome substring is a non-empty substring of s such that we can make any number of swaps in order to make it a palindrome. Return the length of the maximum length awesome substring of s. Example 1: Input: s = "3242415" Output: 5 Explanation: "24241" is the longest awesome substring, we can form the palindrome "24142" with some swaps. Example 2: Input: s = "12345678" Output: 1 Example 3: Input: s = "213123" Output: 6 Explanation: "213123" is the longest awesome substring, we can form the palindrome "231132" with some swaps. Constraints: 1 <= s.length <= 105 s consists only of digits.

Explanation

Here's a solution to find the length of the maximum length awesome substring of a given string, focusing on efficiency and optimality:

• Key Idea: A substring can be rearranged into a palindrome if and only if the count of each digit is even, or at most one digit has an odd count. We use a bitmask to represent the parity (even/odd) of each digit's count. We iterate through the string, updating the bitmask, and use a dictionary to store the first occurrence of each bitmask.
• Leverage Bit Manipulation: Bit manipulation allows us to efficiently represent and update the parity of digit counts. Each bit in the mask corresponds to a digit (0-9).

• Early Occurrence Tracking: The first occurrence of each bitmask determines the start of an awesome substring, so we store only the earliest position of each mask.

• Runtime and Space Complexity: O(n), where n is the length of the input string. Space complexity is O(1) because the maximum possible number of distinct masks is 2^10 which is constant.

Code

    def longestAwesome(s: str) -> int:
    """
    Finds the length of the longest awesome substring of s.

    An awesome substring is a non-empty substring of s such that we can
    make any number of swaps in order to make it a palindrome.

    Args:
        s: The input string consisting of digits.

    Returns:
        The length of the maximum length awesome substring of s.
    """

    first_occurrence = {0: -1}  # Store the first occurrence of each mask
    mask = 0
    max_len = 0

    for i, digit in enumerate(s):
        digit = int(digit)
        mask ^= (1 << digit)  # Update the mask with the parity of the digit

        if mask in first_occurrence:
            max_len = max(max_len, i - first_occurrence[mask])
        else:
            first_occurrence[mask] = i

        # Check for substrings with at most one odd count
        for j in range(10):
            potential_mask = mask ^ (1 << j)
            if potential_mask in first_occurrence:
                max_len = max(max_len, i - first_occurrence[potential_mask])

    return max_len