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Author: jimit105

2463-minimum-recolors-to-get-k-consecutive-black-blocks/README.md

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+<p>You are given a <strong>0-indexed</strong> string <code>blocks</code> of length <code>n</code>, where <code>blocks[i]</code> is either <code>&#39;W&#39;</code> or <code>&#39;B&#39;</code>, representing the color of the <code>i<sup>th</sup></code> block. The characters <code>&#39;W&#39;</code> and <code>&#39;B&#39;</code> denote the colors white and black, respectively.</p>
+
+<p>You are also given an integer <code>k</code>, which is the desired number of <strong>consecutive</strong> black blocks.</p>
+
+<p>In one operation, you can <strong>recolor</strong> a white block such that it becomes a black block.</p>
+
+<p>Return<em> the <strong>minimum</strong> number of operations needed such that there is at least <strong>one</strong> occurrence of </em><code>k</code><em> consecutive black blocks.</em></p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> blocks = &quot;WBBWWBBWBW&quot;, k = 7
+<strong>Output:</strong> 3
+<strong>Explanation:</strong>
+One way to achieve 7 consecutive black blocks is to recolor the 0th, 3rd, and 4th blocks
+so that blocks = &quot;BBBBBBBWBW&quot;. 
+It can be shown that there is no way to achieve 7 consecutive black blocks in less than 3 operations.
+Therefore, we return 3.
+</pre>
+
+<p><strong class="example">Example 2:</strong></p>
+
+<pre>
+<strong>Input:</strong> blocks = &quot;WBWBBBW&quot;, k = 2
+<strong>Output:</strong> 0
+<strong>Explanation:</strong>
+No changes need to be made, since 2 consecutive black blocks already exist.
+Therefore, we return 0.
+</pre>
+
+<p>&nbsp;</p>
+<p><strong>Constraints:</strong></p>
+
+<ul>
+	<li><code>n == blocks.length</code></li>
+	<li><code>1 &lt;= n &lt;= 100</code></li>
+	<li><code>blocks[i]</code> is either <code>&#39;W&#39;</code> or <code>&#39;B&#39;</code>.</li>
+	<li><code>1 &lt;= k &lt;= n</code></li>
+</ul>

2463-minimum-recolors-to-get-k-consecutive-black-blocks/solution.py

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+# Approach: Sliding Window
+
+# Time: O(n)
+# Space: O(1)
+
+class Solution:
+    def minimumRecolors(self, blocks: str, k: int) -> int:
+        curr_white = blocks[:k].count('W')
+
+        min_operations = curr_white
+
+        for i in range(k, len(blocks)):
+            # Remove the contribution of the leftmost character
+            if blocks[i - k] == 'W':
+                curr_white -= 1
+
+            if blocks[i] == 'W':
+                curr_white += 1
+
+            min_operations = min(min_operations, curr_white)
+
+        return min_operations
+