problems(kt): add “2264. Largest 3-Same-Digit Number in String”

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/kt/largest-3-same-digit-number-in-string.kt

@@ -0,0 +1,14 @@
+class Solution {
+    fun largestGoodInteger(num: String): String = num
+        .asSequence()
+        .windowed(3)
+        .filter { s ->
+            s[0] == s[1] && s[1] == s[2]
+        }
+        .map { window ->
+            window.joinToString("")
+        }
+        .maxByOrNull { num ->
+            num.toInt()
+        } ?: ""
+}