Create 138-copy-list-with-random-pointer.js

Author: everthis

138-copy-list-with-random-pointer.js

@@ -0,0 +1,55 @@
+/**
+ * Definition for singly-linked list with a random pointer.
+ * function RandomListNode(label) {
+ *     this.label = label;
+ *     this.next = this.random = null;
+ * }
+ */
+
+/**
+ * @param {RandomListNode} head
+ * @return {RandomListNode}
+ */
+const copyRandomList = function(head) {
+      if (head == null) {
+        return null;
+      }
+  
+      // Creating a new weaved list of original and copied nodes.
+      let ptr = head;
+      while (ptr != null) {
+  
+        // Cloned node
+        const newNode = new RandomListNode(ptr.label);
+  
+        // Inserting the cloned node just next to the original node.
+        // If A->B->C is the original linked list,
+        // Linked list after weaving cloned nodes would be A->A'->B->B'->C->C'
+        newNode.next = ptr.next;
+        ptr.next = newNode;
+        ptr = newNode.next;
+      }
+  
+      ptr = head;
+  
+      // Now link the random pointers of the new nodes created.
+      // Iterate the newly created list and use the original nodes' random pointers,
+      // to assign references to random pointers for cloned nodes.
+      while (ptr != null) {
+        ptr.next.random = (ptr.random != null) ? ptr.random.next : null;
+        ptr = ptr.next.next;
+      }
+  
+      // Unweave the linked list to get back the original linked list and the cloned list.
+      // i.e. A->A'->B->B'->C->C' would be broken to A->B->C and A'->B'->C'
+      let ptr_old_list = head; // A->B->C
+      let ptr_new_list = head.next; // A'->B'->C'
+      let head_old = head.next;
+      while (ptr_old_list != null) {
+        ptr_old_list.next = ptr_old_list.next.next;
+        ptr_new_list.next = (ptr_new_list.next != null) ? ptr_new_list.next.next : null;
+        ptr_old_list = ptr_old_list.next;
+        ptr_new_list = ptr_new_list.next;
+      }
+      return head_old;
+};