Leetcode 2379. Minimum Recolors to Get K Consecutive Black Block

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 = 7Output: 3Explanation: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 = 2Output: 0Explanation: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

使用前缀和的时候，要多一个位置，这也是就一直没解决的原因，尴尬；

同时也可以使用sliding window来解决；

Runtime: 1 ms, faster than 85.02% of Java online submissions for Minimum Recolors to Get K Consecutive Black Blocks.

Memory Usage: 40.4 MB, less than 52.26% of Java online submissions for Minimum Recolors to Get K Consecutive Black Blocks.