学步园

Algorithm: Iterate and copy the original list first. For the random pointer, just copy the value from the original list first. And use a map to store each node's old address and its corresponding new address. After the iteration,
we can replace the value of the random pointer based on the map we get.

Mistakes I make:

  (1) Beware when head == null.

  (2) Forget during the iteration: node = node.next;

public class Solution {
    public RandomListNode copyRandomList(RandomListNode head) {
        if(head == null)
    		return null;
    	RandomListNode newHead = new RandomListNode(head.label);
    	newHead.random = head.random;
    	RandomListNode node = newHead;
    	Map<RandomListNode,RandomListNode> addrRef = new HashMap<RandomListNode,RandomListNode>();
    	
    	addrRef.put(head, node);
    	head = head.next;
    	
    	while(head != null)
    	{
    		RandomListNode tnode = new RandomListNode(head.label);
    		tnode.random = head.random;
    		node.next = tnode;
    		
        	addrRef.put(head, tnode);

    		head = head.next;
    		node = tnode;
    	}
    	
    	node = newHead;
    	while(node != null)
    	{
    		node.random = addrRef.get(node.random);
    		node = node.next;
    	}
    	
    	return newHead;
    	
    }
}