kt: add «2401. Longest Nice Subarray»

URL:	https://leetcode.com/problems/longest-nice-subarray/
Signed-off-by: Matej Focko <me@mfocko.xyz>

kt/longest-nice-subarray.kt

@@ -0,0 +1,26 @@
+class Solution {
+    private data class Acc(var used: Int, var start: Int, val max: Int) {
+        constructor() : this(0, 0, 0)
+
+        fun update(
+            nums: IntArray,
+            end: IndexedValue<Int>,
+        ): Acc {
+            // shrink from left until conflict gets resolved
+            while (used.and(end.value) != 0) {
+                used = used.xor(nums[start])
+                ++start
+            }
+
+            return copy(
+                used = used.or(end.value),
+                max = maxOf(max, end.index - start + 1),
+            )
+        }
+    }
+
+    fun longestNiceSubarray(nums: IntArray): Int =
+        nums.withIndex().fold(Acc()) { acc, end ->
+            acc.update(nums, end)
+        }.max
+}