problems: add maximum units on a truck

problems/maximum-units-on-a-truck.kt

@@ -0,0 +1,19 @@
+class Solution {
+    data class BoxType(val boxes: Int, val units: Int)
+    fun toBoxType(x: IntArray): BoxType = BoxType(x[0], x[1])
+
+    fun maximumUnits(boxTypes: Array<IntArray>, truckSize: Int): Int =
+        boxTypes
+        .map { toBoxType(it) }
+        .sortedByDescending(BoxType::units)
+        .fold(0 to 0) { acc, boxType ->
+            if (acc.first < truckSize) {
+                val count = minOf(truckSize - acc.first, boxType.boxes)
+                
+                (acc.first + count) to (acc.second + count * boxType.units)
+            } else {
+                acc
+            }
+        }
+        .second
+}