Introduction

In this blog post, we will explore how to solve the LeetCode problem "2379" 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 0-indexed string blocks of length n, where blocks[i] is either 'W' or 'B', representing the color of the ith block. The characters 'W' and 'B' denote the colors white and black, respectively. You are also given an integer k, which is the desired number of consecutive black blocks. In one operation, you can recolor a white block such that it becomes a black block. Return the minimum number of operations needed such that there is at least one occurrence of k consecutive black blocks. Example 1: Input: blocks = "WBBWWBBWBW", k = 7 Output: 3 Explanation: One way to achieve 7 consecutive black blocks is to recolor the 0th, 3rd, and 4th blocks so that blocks = "BBBBBBBWBW". It can be shown that there is no way to achieve 7 consecutive black blocks in less than 3 operations. Therefore, we return 3. Example 2: Input: blocks = "WBWBBBW", k = 2 Output: 0 Explanation: No changes need to be made, since 2 consecutive black blocks already exist. Therefore, we return 0. Constraints: n == blocks.length 1 <= n <= 100 blocks[i] is either 'W' or 'B'. 1 <= k <= n

Explanation

Here's a breakdown of the solution:

• Sliding Window: Use a sliding window of size k to iterate through the blocks string.
• Count White Blocks: Within each window, count the number of white blocks ('W'). This represents the number of operations needed to make that window all black.

• Minimize Operations: Keep track of the minimum number of white blocks encountered across all windows.

• Runtime Complexity: O(n) & Storage Complexity: O(1)

Code

    def min_recolors(blocks: str, k: int) -> int:
    """
    Calculates the minimum number of operations needed to have k consecutive black blocks.

    Args:
        blocks: The string representing the colors of the blocks.
        k: The desired number of consecutive black blocks.

    Returns:
        The minimum number of operations needed.
    """

    n = len(blocks)
    min_ops = float('inf')
    white_count = 0

    # Initialize the first window
    for i in range(k):
        if blocks[i] == 'W':
            white_count += 1

    min_ops = white_count

    # Slide the window
    for i in range(k, n):
        if blocks[i] == 'W':
            white_count += 1
        if blocks[i - k] == 'W':
            white_count -= 1
        min_ops = min(min_ops, white_count)

    return min_ops