Introduction

In this blog post, we will explore how to solve the LeetCode problem "738" 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

An integer has monotone increasing digits if and only if each pair of adjacent digits x and y satisfy x <= y. Given an integer n, return the largest number that is less than or equal to n with monotone increasing digits. Example 1: Input: n = 10 Output: 9 Example 2: Input: n = 1234 Output: 1234 Example 3: Input: n = 332 Output: 299 Constraints: 0 <= n <= 109

Explanation

Here's the breakdown of the problem and the optimal solution:

• High-Level Approach:

  • Iterate from the most significant digit to the least significant digit.
  • If a digit is greater than the digit to its right, decrement the digit and change all subsequent digits to 9.
  • Handle potential carry-over effects of decrementing a digit (e.g., 10 -> 9, leading to 09) by propagating the decrement to the left.

• Complexity:

  • Runtime: O(log n) - proportional to the number of digits in n.
  • Storage: O(log n) - to store the digits of n.

Code

    def monotoneIncreasingDigits(n: int) -> int:
    s = list(str(n))
    length = len(s)

    for i in range(length - 1, 0, -1):
        if s[i] < s[i - 1]:
            s[i - 1] = str(int(s[i - 1]) - 1)
            for j in range(i, length):
                s[j] = '9'

    # Handle leading zeros after decrementing.  This is crucial!  Without this the solution will be incorrect.
    i = 0
    while i < length - 1 and s[i] == '0':
        i += 1

    return int("".join(s[i:]))