kt: add «2379. Minimum Recolors to Get K Consecutive Black Blocks»

URL:	https://leetcode.com/problems/minimum-recolors-to-get-k-consecutive-black-blocks/
Signed-off-by: Matej Focko <me@mfocko.xyz>

kt/minimum-recolors-to-get-k-consecutive-black-blocks.kt

@@ -0,0 +1,35 @@
+class Solution {
+    private data class Acc(var l: Int, var white: Int, var recolors: Int) {
+        constructor() : this(0, 0, Int.MAX_VALUE)
+
+        fun update(
+            blocks: String,
+            k: Int,
+            c: IndexedValue<Char>,
+        ): Acc {
+            if (c.value == 'W') {
+                white++
+            }
+
+            if (c.index - l + 1 == k) {
+                recolors = minOf(recolors, white)
+
+                if (blocks[l] == 'W') {
+                    white--
+                }
+
+                l++
+            }
+
+            return this
+        }
+    }
+
+    fun minimumRecolors(
+        blocks: String,
+        k: Int,
+    ): Int =
+        blocks.toCharArray().withIndex().fold(Acc()) { acc, c ->
+            acc.update(blocks, k, c)
+        }.recolors
+}