Create Deep copy linked list with random pointer.java

Deep copy linked list with random pointer.java

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+/*
+Each of the nodes in the linked list has another pointer pointing to a random node in the list or null. 
+Make a deep copy of the original list.
+
+time = O(n)
+space = O(n)    hashmap to avoid duplication
+*/
+
+/**
+ * class ListNode {
+ *   public int value;
+ *   public ListNode next;
+ *   public ListNode(int value) {
+ *     this.value = value;
+ *     next = null;
+ *   }
+ * }
+ */
+public class Solution {
+  public RandomListNode copy(RandomListNode head) {
+    // Write your solution here
+    if (head == null) {
+    	return head;
+    }
+    RandomListNode dummy = new RandomListNode(0);
+    RandomListNode cur = dummy;
+    Map<RandomListNode, RandomListNode> map = new HashMap<>();
+    while (head != null) {
+    	if (!map.containsKey(head)) {
+        map.put(head, new RandomListNode(head.value));
+      }
+      cur.next = map.get(head);
+      if (head.random != null) {
+      	if (!map.containsKey(head.random)) {
+        	map.put(head.random, new RandomListNode(head.random.value));
+        }
+        cur.next.random = map.get(head.random);
+      }
+      head = head.next;
+      cur = cur.next;
+    }
+    return dummy.next;
+  }
+}