Introduction

In this blog post, we will explore how to solve the LeetCode problem "3174" 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. Your task is to remove all digits by doing this operation repeatedly: Delete the first digit and the closest non-digit character to its left. Return the resulting string after removing all digits. Note that the operation cannot be performed on a digit that does not have any non-digit character to its left. Example 1: Input: s = "abc" Output: "abc" Explanation: There is no digit in the string. Example 2: Input: s = "cb34" Output: "" Explanation: First, we apply the operation on s[2], and s becomes "c4". Then we apply the operation on s[1], and s becomes "". Constraints: 1 <= s.length <= 100 s consists only of lowercase English letters and digits. The input is generated such that it is possible to delete all digits.

Explanation

Here's a breakdown of the approach and the Python code:

• High-Level Approach:

  • Iterate through the string from left to right.
  • Use a stack to keep track of non-digit characters encountered so far.
  • When a digit is encountered, pop the last non-digit character from the stack (if it exists). If the stack is empty, it means the digit cannot be removed based on the rules, which violates the constraint that such situation will not happen.

• Complexity:

  • Runtime Complexity: O(n), where n is the length of the string.
  • Storage Complexity: O(n) in the worst-case scenario where the string contains only non-digit characters.

Code

    def remove_digits(s: str) -> str:
    """
    Removes all digits from the string s by repeatedly deleting the first digit and the closest non-digit character to its left.

    Args:
        s: The input string containing lowercase English letters and digits.

    Returns:
        The resulting string after removing all digits.
    """

    stack = []
    for char in s:
        if char.isdigit():
            stack.pop()  # Remove the closest non-digit character
        else:
            stack.append(char)  # Add non-digit character to the stack

    return "".join(stack)