Added CopyWithRandomLink.java

leetcode/CopyListWithRandomLink.java

@@ -0,0 +1,54 @@
+/**
+ * Leetcode 138.
+ *  
+ * A linked list is given such that each node contains 
+ * an additional random pointer which could point to any node in the list or null.
+ *
+ * Return a deep copy of the list. 
+ *
+ * Definition for singly-linked list with a random pointer.
+ * class RandomListNode {
+ *     int label;
+ *     RandomListNode next, random;
+ *     RandomListNode(int x) { this.label = x; }
+ * };
+ */
+public class CopyListWithRandomLink {
+    public RandomListNode copyRandomList(RandomListNode head) {
+        if (head == null) {
+            return head;
+        }
+
+        // Generate copied node and embeded to the exist list
+        RandomListNode curr = head;
+        while (curr != null) {
+            RandomListNode nd = new RandomListNode(curr.label);
+            nd.next = curr.next;
+            curr.next = nd;
+            curr = nd.next;
+        }
+
+        // Generate Random link in the mixed list
+        curr = head;
+        while (curr != null) {
+            if (curr.random != null) {
+                // curr.next is the new curr
+                // curr.random is old random. curr.random.next is the new random
+                curr.next.random = curr.random.next;
+            }
+            curr = curr.next.next;
+        }
+
+        // split the list and recover existing list
+        RandomListNode newHead = new RandomListNode(-1);
+        RandomListNode newCurr = newHead;
+        curr = head;
+        while (curr != null) {
+            newCurr.next = curr.next;
+            newCurr = newCurr.next;
+            curr.next = curr.next.next;
+            curr = curr.next;
+        }
+        return newHead.next;
+    }
+}