Introduction

In this blog post, we will explore how to solve the LeetCode problem "2165" 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 an integer num. Rearrange the digits of num such that its value is minimized and it does not contain any leading zeros. Return the rearranged number with minimal value. Note that the sign of the number does not change after rearranging the digits. Example 1: Input: num = 310 Output: 103 Explanation: The possible arrangements for the digits of 310 are 013, 031, 103, 130, 301, 310. The arrangement with the smallest value that does not contain any leading zeros is 103. Example 2: Input: num = -7605 Output: -7650 Explanation: Some possible arrangements for the digits of -7605 are -7650, -6705, -5076, -0567. The arrangement with the smallest value that does not contain any leading zeros is -7650. Constraints: -1015 <= num <= 1015

Explanation

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

• Approach:

  • Determine the sign of the number.
  • Count the frequency of each digit. Arrange digits in ascending order, but handle leading zeros carefully by placing the smallest non-zero digit first.
  • If the number is negative, arrange the digits in descending order after the sign.

• Complexity:

  • Runtime Complexity: O(n), where n is the number of digits in the input number.
  • Storage Complexity: O(1), as we use a fixed-size array (digit counts).

Code

    def rearrange_digits(num: int) -> int:
    """Rearranges digits of num to minimize its value without leading zeros."""

    sign = 1 if num >= 0 else -1
    num = abs(num)
    counts = [0] * 10
    for digit_char in str(num):
        counts[int(digit_char)] += 1

    if sign == 1:
        result = ""
        first_non_zero = -1
        for i in range(1, 10):
            if counts[i] > 0:
                first_non_zero = i
                break

        if first_non_zero == -1:
            return 0  # num was 0

        result += str(first_non_zero)
        counts[first_non_zero] -= 1

        for i in range(10):
            result += str(i) * counts[i]

        return int(result) * sign
    else:
        result = ""
        for i in range(9, -1, -1):
            result += str(i) * counts[i]
        return int(result) * sign