Kotlin - Change Complete

kotlin/change/src/main/kotlin/Change.kt

@@ -1,10 +1,11 @@
 class Change(val setOfCoins: Set<Int>) {
-    fun issue(x: Int): List<Int>{
+    // This is a good greedy implementation of the algorithm
+    fun issue_greedy(x: Int): List<Int> {
         require((x > setOfCoins.min()!!) or (x == 0))
         var y = x
         val returnList = mutableListOf<Int>()
-        
+
-        while (y != 0){
+        while (y != 0) {
             val maxChange = setOfCoins.filter { y >= it }.max()
             returnList.add(maxChange ?: 0)
             y -= maxChange ?: 0
@@ -12,4 +13,35 @@ class Change(val setOfCoins: Set<Int>) {
 
         return returnList.reversed()
     }
+
+    val resultMap: MutableMap<Int, List<Int>> = mutableMapOf<Int, List<Int>>()
+
+    fun issue(x: Int): List<Int> {
+        require((x >= setOfCoins.min()!!) or (x == 0))
+        if (x == 0) {
+            return emptyList()
+        } else if (x in setOfCoins) {
+            return listOf(x)
+        } else if (x in resultMap){
+            return resultMap[x]!!
+        } else {
+            for (i in setOfCoins.filter { it <= x }) {
+                val firstCandidate = issue(x - i) + i
+                if (resultMap[x]?.isEmpty() ?: true){
+                    resultMap[x] = firstCandidate
+                }
+                if (firstCandidate.size < resultMap[x]?.size ?: 1000){
+                    resultMap[x] = firstCandidate
+                }
+            }
+        }
+
+        return resultMap[x]!!.sorted()
+    }
+}
+
+
+fun main(args: Array<String>) {
+    print(Change(setOf(1, 5, 10, 21, 25)).issue(63))
+    print(Change(setOf(1, 4, 15, 20, 50)).issue(23))
 }