kt: add «2501. Longest Square Streak in an Array»

URL:	https://leetcode.com/problems/longest-square-streak-in-an-array/
Signed-off-by: Matej Focko <me@mfocko.xyz>

kt/longest-square-streak-in-an-array.kt

@@ -0,0 +1,15 @@
+class Solution {
+    fun longestSquareStreak(nums: IntArray): Int {
+        nums.sort()
+
+        val foundBest = mutableMapOf<Int, Int>()
+        for (num in nums) {
+            val squared = num * num
+            foundBest.put(squared, 1 + foundBest.getOrDefault(num, 0))
+        }
+
+        return foundBest.values.filter {
+            it >= 2
+        }.maxOrNull() ?: -1
+    }
+}