Introduction

In this blog post, we will explore how to solve the LeetCode problem "1694" 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 phone number as a string number. number consists of digits, spaces ' ', and/or dashes '-'. You would like to reformat the phone number in a certain manner. Firstly, remove all spaces and dashes. Then, group the digits from left to right into blocks of length 3 until there are 4 or fewer digits. The final digits are then grouped as follows: 2 digits: A single block of length 2. 3 digits: A single block of length 3. 4 digits: Two blocks of length 2 each. The blocks are then joined by dashes. Notice that the reformatting process should never produce any blocks of length 1 and produce at most two blocks of length 2. Return the phone number after formatting. Example 1: Input: number = "1-23-45 6" Output: "123-456" Explanation: The digits are "123456". Step 1: There are more than 4 digits, so group the next 3 digits. The 1st block is "123". Step 2: There are 3 digits remaining, so put them in a single block of length 3. The 2nd block is "456". Joining the blocks gives "123-456". Example 2: Input: number = "123 4-567" Output: "123-45-67" Explanation: The digits are "1234567". Step 1: There are more than 4 digits, so group the next 3 digits. The 1st block is "123". Step 2: There are 4 digits left, so split them into two blocks of length 2. The blocks are "45" and "67". Joining the blocks gives "123-45-67". Example 3: Input: number = "123 4-5678" Output: "123-456-78" Explanation: The digits are "12345678". Step 1: The 1st block is "123". Step 2: The 2nd block is "456". Step 3: There are 2 digits left, so put them in a single block of length 2. The 3rd block is "78". Joining the blocks gives "123-456-78". Constraints: 2 <= number.length <= 100 number consists of digits and the characters '-' and ' '. There are at least two digits in number.

Explanation

Here's a breakdown of the approach, followed by the Python code:

• Clean the input: Remove spaces and dashes to get a string of only digits.
• Iterative grouping: Group digits into blocks of 3 until 4 or fewer digits remain.

• Handle remaining digits: Group the final digits according to the specified rules (2, 3, or two groups of 2).

• Runtime Complexity: O(n), where n is the length of the input string.

• Storage Complexity: O(n), for storing the cleaned number and the formatted result.

Code

    def reformat_number(number: str) -> str:
    """
    Reformats a phone number string according to the problem description.
    """
    digits = "".join(c for c in number if c.isdigit())
    n = len(digits)
    result = []
    i = 0
    while n - i > 4:
        result.append(digits[i:i+3])
        i += 3

    if n - i == 2:
        result.append(digits[i:])
    elif n - i == 3:
        result.append(digits[i:])
    elif n - i == 4:
        result.append(digits[i:i+2])
        result.append(digits[i+2:])

    return "-".join(result)