Introduction

In this blog post, we will explore how to solve the LeetCode problem "75" 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

Given an array nums with n objects colored red, white, or blue, sort them in-place so that objects of the same color are adjacent, with the colors in the order red, white, and blue. We will use the integers 0, 1, and 2 to represent the color red, white, and blue, respectively. You must solve this problem without using the library's sort function. Example 1: Input: nums = [2,0,2,1,1,0] Output: [0,0,1,1,2,2] Example 2: Input: nums = [2,0,1] Output: [0,1,2] Constraints: n == nums.length 1 <= n <= 300 nums[i] is either 0, 1, or 2. Follow up: Could you come up with a one-pass algorithm using only constant extra space?

Explanation

Here's the breakdown of the approach and the Python code for the Dutch National Flag algorithm:

• Dutch National Flag Algorithm: This problem is a classic application of the Dutch National Flag algorithm. We maintain three pointers: low, mid, and high. The low pointer keeps track of the boundary between the 0s and the 1s, the mid pointer iterates through the array, and the high pointer keeps track of the boundary between the 2s and the 1s.
• In-place Sorting: The algorithm sorts the array in-place by swapping elements based on their values.

• One-Pass: It achieves the sorting in a single pass through the array.

• Runtime & Storage Complexity: O(n) runtime, O(1) storage.

Code

    def sortColors(nums: list[int]) -> None:
    """
    Sorts an array of 0s, 1s, and 2s in-place.

    Args:
        nums: A list of integers representing colors (0, 1, or 2).
    """
    low = 0
    mid = 0
    high = len(nums) - 1

    while mid <= high:
        if nums[mid] == 0:
            nums[low], nums[mid] = nums[mid], nums[low]
            low += 1
            mid += 1
        elif nums[mid] == 1:
            mid += 1
        else:
            nums[mid], nums[high] = nums[high], nums[mid]
            high -= 1