LeetCode OJ

参考了一个前辈的算法，能够在O(n)的时间复杂度，O(1)的空间复杂度内解决这个问题。 算法过程如下图所示。总共有三个步骤：

下面是AC代码：

class RandomListNode{
    int label;
    RandomListNode next, random;
    RandomListNode(int x){ this.label = x;}
}

/**
     * deep copy with random pointer
     * @param head
     * @return
     */
    public RandomListNode copyRandomList(RandomListNode head){
        if(head == null )
            return null;
        RandomListNode p = head;
        do{
            RandomListNode q = p.next;
            p.next = new RandomListNode(p.label);
            p.next.next = q;
            p = q;
        }while(p!=null);
        
        p = head;
        do{
            RandomListNode q = p.next.next;
            p.next.random = p.random == null? null: p.random.next;
            p = q;
        }while(p!=null);
        
        p=head;
        RandomListNode q = p.next;
        RandomListNode ch = p.next;
        RandomListNode r = ch;
        while(true)
        {
            p.next = q.next;
            r.next = q.next== null? null:q.next.next;
            if(q.next==null)
                break;
            q=r.next;
            r = q;
            p = p.next;
        }
            
        return ch;
    }