Improved task 138

src/main/kotlin/com_github_leetcode/random/Node.kt

@@ -7,20 +7,10 @@ class Node {
     var next: Node? = null
     var random: Node? = null
 
-    constructor() {
-        `val` = 0
-    }
-
     constructor(`val`: Int) {
         this.`val` = `val`
     }
 
-    constructor(`val`: Int, next: Node?, random: Node?) {
-        this.`val` = `val`
-        this.next = next
-        this.random = random
-    }
-
     override fun toString(): String {
         val result = StringJoiner(",", "[", "]")
         val result2 = StringJoiner(",", "[", "]")

src/main/kotlin/g0101_0200/s0138_copy_list_with_random_pointer/Solution.kt

@@ -2,7 +2,7 @@ package g0101_0200.s0138_copy_list_with_random_pointer
 
 // #Medium #Top_100_Liked_Questions #Top_Interview_Questions #Hash_Table #Linked_List
 // #Programming_Skills_II_Day_14 #Udemy_Linked_List #Top_Interview_150_Linked_List
-// #Big_O_Time_O(N)_Space_O(N) #2022_09_03_Time_274_ms_(80.58%)_Space_40.5_MB_(58.99%)
+// #Big_O_Time_O(N)_Space_O(N) #2025_07_04_Time_123_ms_(90.70%)_Space_43.99_MB_(97.67%)
 
 import com_github_leetcode.random.Node
 
@@ -18,48 +18,19 @@ import com_github_leetcode.random.Node
  */
 class Solution {
     fun copyRandomList(head: Node?): Node? {
-        if (head == null) {
-            return null
+        val hashMap: MutableMap<Node?, Node> = HashMap()
+        var cur = head
+        while (cur != null) {
+            hashMap.put(cur, Node(cur.`val`))
+            cur = cur.next
         }
-        // first pass to have a clone node point to the next node. ie A->B becomes A->clonedNode->B
-        var curr: Node? = head
-        while (curr != null) {
-            val clonedNode = Node(curr.`val`)
-            clonedNode.next = curr.next
-            curr.next = clonedNode
-            curr = clonedNode.next
+        cur = head
+        while (cur != null) {
+            val copy: Node = hashMap[cur]!!
+            copy.next = hashMap[cur.next]
+            copy.random = hashMap[cur.random]
+            cur = cur.next
         }
-        curr = head
-        // second pass to make the cloned node's random pointer point to the orginal node's randome
-        // pointer.
-        // ie. A's random pointer becomes ClonedNode's random pointer
-        while (curr != null) {
-            if (curr.random != null) {
-                curr.next?.random = curr.random!!.next
-            } else {
-                curr.next?.random = null
-            }
-            curr = curr.next?.next
-        }
-        curr = head
-        // third pass to restore the links and return the head of the cloned nodes' list.
-        var newHead: Node? = null
-        while (curr != null) {
-            var clonedNode: Node
-            if (newHead == null) {
-                clonedNode = curr.next!!
-                newHead = clonedNode
-            } else {
-                clonedNode = curr.next!!
-            }
-            curr.next = clonedNode.next
-            if (curr.next != null) {
-                clonedNode.next = curr.next!!.next
-            } else {
-                clonedNode.next = null
-            }
-            curr = curr.next
-        }
-        return newHead
+        return hashMap[head]
     }
 }

src/test/kotlin/com_github_leetcode/random/NodeTest.kt

@@ -7,7 +7,7 @@ import org.junit.jupiter.api.Test
 internal class NodeTest {
     @Test
     fun constructor() {
-        val node = Node()
+        val node = Node(0)
         assertThat(node.`val`, equalTo(0))
         assertThat(node.toString(), equalTo("[[0,null]]"))
     }
@@ -21,18 +21,23 @@ internal class NodeTest {
 
     @Test
     fun constructor3() {
-        val node = Node(1, Node(2), Node(3))
+        val node = Node(1)
+        node.next = Node(2)
+        node.random = Node(3)
         assertThat(node.`val`, equalTo(1))
         assertThat(node.toString(), equalTo("[[1,3],[2,null]]"))
     }
 
     @Test
     fun constructor4() {
-        val node = Node(
-            1,
-            Node(2, Node(21), Node(22)),
-            Node(3, null, Node(32)),
-        )
+        val next = Node(2)
+        next.next = Node(21)
+        next.random = Node(22)
+        val random = Node(3)
+        random.random = Node(32)
+        val node = Node(1)
+        node.next = next
+        node.random = random
         assertThat(node.`val`, equalTo(1))
         assertThat(node.toString(), equalTo("[[1,3],[2,2],[21,null]]"))
     }

src/test/kotlin/g0101_0200/s0138_copy_list_with_random_pointer/SolutionTest.kt

@@ -23,7 +23,10 @@ internal class SolutionTest {
         node11.random = node1
         node10.random = node11
         node1.random = node7
-        assertThat(Solution().copyRandomList(node7).toString(), equalTo("[[7,null],[13,0],[11,4],[10,2],[1,0]]"))
+        assertThat(
+            Solution().copyRandomList(node7).toString(),
+            equalTo("[[7,null],[13,0],[11,4],[10,2],[1,0]]"),
+        )
     }
 
     @Test
@@ -34,7 +37,10 @@ internal class SolutionTest {
         node1.random = node1
         node2.next = null
         node2.random = node2
-        assertThat(Solution().copyRandomList(node1).toString(), equalTo("[[1,1],[2,1]]"))
+        assertThat(
+            Solution().copyRandomList(node1).toString(),
+            equalTo("[[1,1],[2,1]]"),
+        )
     }
 
     @Test
@@ -48,6 +54,9 @@ internal class SolutionTest {
         node32.random = node31
         node33.next = null
         node33.random = null
-        assertThat(Solution().copyRandomList(node31).toString(), equalTo("[[3,null],[3,0],[3,null]]"))
+        assertThat(
+            Solution().copyRandomList(node31).toString(),
+            equalTo("[[3,null],[3,0],[3,null]]"),
+        )
     }
 }