kt: add «12. Integer to Roman»

URL:	https://leetcode.com/problems/integer-to-roman/
Signed-off-by: Matej Focko <me@mfocko.xyz>

kt/integer-to-roman.kt

@@ -0,0 +1,36 @@
+class Solution {
+    companion object {
+        private val SYMBOLS: List<Pair<Int, String>> =
+            listOf(
+                1000 to "M",
+                900 to "CM",
+                500 to "D",
+                400 to "CD",
+                100 to "C",
+                90 to "XC",
+                50 to "L",
+                40 to "XL",
+                10 to "X",
+                9 to "IX",
+                5 to "V",
+                4 to "IV",
+                1 to "I",
+            )
+    }
+
+    fun intToRoman(num: Int): String =
+        SYMBOLS.fold(num to StringBuilder()) { (num, sb), (value, symbol) ->
+            when (num) {
+                0 -> num to sb
+                else -> {
+                    val count = num / value
+
+                    (1..count).forEach {
+                        sb.append(symbol)
+                    }
+
+                    num % value to sb
+                }
+            }
+        }.second.toString()
+}