Refactor ListNode

Author: juchanei

jvm/src/main/java/io/github/juchanei/leetcodeJava/ListNode.kt

@@ -0,0 +1,28 @@
+package io.github.juchanei.leetcodeJava
+
+data class ListNode(val `val`: Int, var next: ListNode?)
+
+fun List<Int>.toListNode(): ListNode? =
+    if (isEmpty()) null else ListNode(first(), drop(1).toListNode())
+
+fun ListNode?.toList(): List<Int> {
+    val result = mutableListOf<Int>()
+
+    var node: ListNode? = this
+    while (true) {
+        if (node == null) break
+        result.add(node.`val`)
+        node = node.next
+    }
+
+    return result
+}
+
+fun ListNode.reversed(): ListNode = reverse(this)
+
+tailrec fun reverse(head: ListNode, acc: ListNode? = null): ListNode =
+    if (head.next == null) {
+        ListNode(head.`val`, acc)
+    } else {
+        reverse(head.next as ListNode, ListNode(head.`val`, acc))
+    }

jvm/src/main/java/io/github/juchanei/leetcodeJava/MergeTwoSortedLists.kt

@@ -5,8 +5,6 @@ import org.junit.jupiter.api.Test
 
 // https://leetcode.com/explore/interview/card/top-interview-questions-easy/93/linked-list/771/
 class MergeTwoSortedLists {
-    data class ListNode(val `val`: Int, val next: ListNode?)
-
     fun mergeTwoLists(list1: ListNode?, list2: ListNode?): ListNode? =
         mergeTwoLists(list1, list2, null)?.reversed()
 
@@ -24,15 +22,6 @@ class MergeTwoSortedLists {
             mergeTwoLists(list1?.next, list2?.next, ListNode(value, acc))
         }
 
-    private fun ListNode.reversed(): ListNode = reverse(this)
-
-    private tailrec fun reverse(head: ListNode, acc: ListNode? = null): ListNode =
-        if (head.next == null) {
-            ListNode(head.`val`, acc)
-        } else {
-            reverse(head.next, ListNode(head.`val`, acc))
-        }
-
     @Test
     fun example1() {
         val l1 = listOf(1, 2, 4)
@@ -76,21 +65,4 @@ class MergeTwoSortedLists {
 
         then(actual.toList()).isEqualTo(expected)
     }
-    private fun List<Int>.toListNode(): ListNode? {
-        if (isEmpty()) return null
-        return ListNode(first(), drop(1).toListNode())
-    }
-
-    private fun ListNode?.toList(): List<Int> {
-        val result = mutableListOf<Int>()
-
-        var node: ListNode? = this
-        while (true) {
-            if (node == null) break
-            result.add(node.`val`)
-            node = node.next
-        }
-
-        return result
-    }
 }

jvm/src/main/java/io/github/juchanei/leetcodeJava/RemoveNthNodeFromEndOfList.kt

@@ -5,8 +5,6 @@ import org.junit.jupiter.api.Test
 
 // https://leetcode.com/explore/interview/card/top-interview-questions-easy/93/linked-list/603/
 class RemoveNthNodeFromEndOfList {
-    class ListNode(var `val`: Int, var next: ListNode? = null)
-
     fun removeNthFromEnd(head: ListNode?, n: Int): ListNode? {
         if (head == null) return null
 
@@ -75,22 +73,4 @@ class RemoveNthNodeFromEndOfList {
 
         then(actual.toList()).isEqualTo(listOf(2))
     }
-
-    private fun List<Int>.toListNode(): ListNode? {
-        if (isEmpty()) return null
-        return ListNode(first(), drop(1).toListNode())
-    }
-
-    private fun ListNode?.toList(): List<Int> {
-        val result = mutableListOf<Int>()
-
-        var node: ListNode? = this
-        while (true) {
-            if (node == null) break
-            result.add(node.`val`)
-            node = node.next
-        }
-
-        return result
-    }
 }

jvm/src/main/java/io/github/juchanei/leetcodeJava/ReverseLinkedList.kt

@@ -5,20 +5,7 @@ import org.junit.jupiter.api.Test
 
 // https://leetcode.com/explore/interview/card/top-interview-questions-easy/93/linked-list/560/
 class ReverseLinkedList {
-    data class ListNode(val `val`: Int, val next: ListNode?)
-
-    fun reverseList(head: ListNode?): ListNode? =
-        reverseList(head = head, acc = null)
-
-    private tailrec fun reverseList(head: ListNode?, acc: ListNode?): ListNode? =
-        if (head == null) {
-            acc
-        } else {
-            reverseList(
-                head = head.next,
-                acc = ListNode(head.`val`, acc)
-            )
-        }
+    fun reverseList(head: ListNode?): ListNode? = head?.reversed()
 
     @Test
     fun example1() {
@@ -55,22 +42,4 @@ class ReverseLinkedList {
 
         then(actual.toList()).isEqualTo(l.reversed())
     }
-
-    private fun List<Int>.toListNode(): ListNode? {
-        if (isEmpty()) return null
-        return ListNode(first(), drop(1).toListNode())
-    }
-
-    private fun ListNode?.toList(): List<Int> {
-        val result = mutableListOf<Int>()
-
-        var node: ListNode? = this
-        while (true) {
-            if (node == null) break
-            result.add(node.`val`)
-            node = node.next
-        }
-
-        return result
-    }
 }