refactor implementation

Author: freemanzhang

src/hashtable/CopyListWithRandomPointer.java

@@ -1,117 +1,107 @@
-package hashtable;
-
-import java.util.HashMap;
-import java.util.Map;
-
-import org.junit.Test;
-
-// Definition for singly-linked list with a random pointer.
- class RandomListNode 
- {
-     int label;
-     RandomListNode next, random;
-     RandomListNode(int x) { this.label = x; }
- };
- 
-public class CopyListWithRandomPointer
-{
-	public RandomListNode copyRandomListHashMap( RandomListNode head )
-	{
-        if ( head == null ) 
-        {
-            return null;
-        }
-
-        Map<RandomListNode, RandomListNode> map = new HashMap<RandomListNode, RandomListNode>();
-        RandomListNode dummy = new RandomListNode(0);
-        RandomListNode pre = dummy, newNode;
-        while ( head != null ) 
-        {
-            if ( map.containsKey( head ) ) 
-            {
-                newNode = map.get( head );
-            } 
-            else 
-            {
-                newNode = new RandomListNode( head.label );
-                map.put( head, newNode );
-            }
-            pre.next = newNode;
-
-            if ( head.random != null ) 
-            {
-                if ( map.containsKey( head.random ) ) 
-                {
-                    newNode.random = map.get( head.random );
-                } 
-                else 
-                {
-                    newNode.random = new RandomListNode( head.random.label );
-                    map.put( head.random, newNode.random );
-                }
-            }
-
-            pre = newNode;
-            head = head.next;
-        }
-
-        return dummy.next;		
-	}
-	
-    public RandomListNode copyRandomList( RandomListNode head )
-    {
-    	if ( head == null )
-    	{
-    		return null;
-    	}
-    	
-    	// create and link next node
-    	RandomListNode currNode = head;
-    	while ( currNode != null )
-    	{
-    		RandomListNode nextNode = currNode.next;
-    		
-    		RandomListNode copiedNode = new RandomListNode( currNode.label );
-    		currNode.next = copiedNode;
-    		copiedNode.next = nextNode;
-    		
-    		currNode = nextNode;
-    	}
-    	
-    	// assign random pointer
-    	currNode = head;
-    	while ( currNode != null )
-    	{
-    		RandomListNode nextNode = currNode.next.next;
-    		
-    		currNode.next.random = currNode.random == null ? null : currNode.random.next;
-    		
-    		currNode = nextNode;
-    	}
-    	
-    	// assign next pointer
-    	RandomListNode copiedHead = head.next;
-    	currNode = head;
-    	RandomListNode currCopiedNode = copiedHead;
-    	while ( currNode != null )
-    	{
-    		RandomListNode nextNode = currCopiedNode.next;
-    		RandomListNode nextCopiedNode = nextNode == null ? null : nextNode.next;
-    		
-    		currNode.next = nextNode;
-    		currCopiedNode.next = nextCopiedNode;
-    		
-    		currNode = nextNode;
-    		currCopiedNode = nextCopiedNode;
-    	}
-    	
-    	return copiedHead;
-    }
-    
-    @Test
-    public void test()
-    {
-    	RandomListNode node = new RandomListNode( 1 );
-    	RandomListNode copiedNode = copyRandomList( node );    	
-    }
-}
+package hashtable;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.Test;
+
+// Definition for singly-linked list with a random pointer.
+ class RandomListNode 
+ {
+     int label;
+     RandomListNode next, random;
+     RandomListNode(int x) { this.label = x; }
+ };
+ 
+public class CopyListWithRandomPointer
+{
+	public RandomListNode copyRandomListHashMap( RandomListNode head )
+	{
+        if ( head == null ) 
+        {
+            return null;
+        }
+
+        Map<RandomListNode, RandomListNode> map = new HashMap<RandomListNode, RandomListNode>();
+        RandomListNode dummyHead = new RandomListNode(0);
+        RandomListNode resultTail = dummyHead, newNode;
+        RandomListNode currNode = head;
+        while ( currNode != null ) 
+        {
+        	// create node
+        	map.putIfAbsent( currNode, new RandomListNode( currNode.label ) );
+        	newNode = map.get( currNode );        	
+
+            // assign random pointer
+            if ( currNode.random != null ) 
+            {
+            	map.putIfAbsent( currNode.random, new RandomListNode( currNode.label ) );
+            	newNode = map.get( currNode.random );        	
+            }
+            
+            // concatenate
+            resultTail.next = newNode;
+            resultTail = newNode;
+            currNode = currNode.next;
+        }
+
+        return dummyHead.next;		
+	}
+	
+    public RandomListNode copyRandomList( RandomListNode head )
+    {
+    	if ( head == null )
+    	{
+    		return null;
+    	}
+    	
+    	// create and link next node
+    	RandomListNode currNode = head;
+    	while ( currNode != null )
+    	{
+    		RandomListNode nextNode = currNode.next;
+    		
+    		RandomListNode copiedNode = new RandomListNode( currNode.label );
+    		currNode.next = copiedNode;
+    		copiedNode.next = nextNode;
+    		
+    		currNode = nextNode;
+    	}
+    	
+    	// assign random pointer
+    	currNode = head;
+    	while ( currNode != null )
+    	{
+    		RandomListNode nextNode = currNode.next.next;
+    		
+    		currNode.next.random = currNode.random == null ? null : currNode.random.next;
+    		
+    		currNode = nextNode;
+    	}
+    	
+    	// assign next pointer
+    	RandomListNode copiedHead = head.next;
+    	currNode = head;
+    	RandomListNode currCopiedNode = copiedHead;
+    	while ( currNode != null )
+    	{
+    		RandomListNode nextNode = currCopiedNode.next;
+    		RandomListNode nextCopiedNode = nextNode == null ? null : nextNode.next;
+    		
+    		currNode.next = nextNode;
+    		currCopiedNode.next = nextCopiedNode;
+    		
+    		currNode = nextNode;
+    		currCopiedNode = nextCopiedNode;
+    	}
+    	
+    	return copiedHead;
+    }
+    
+    @Test
+    public void test()
+    {
+    	RandomListNode node = new RandomListNode( 1 );
+    	RandomListNode copiedNode = copyRandomList( node );    	
+    }
+}