Copy List with Random Pointer

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.

解决思路首先想到的还是把链表当做有向图来深度遍历，

但是要特别注意的地方是他可能会有自环

public RandomListNode dfs(RandomListNode node, Map<Integer, RandomListNode> vis) {
        if (node != null && vis.get(node.label) == null) {

            RandomListNode cloneNode = new RandomListNode(node.label);

            vis.put(node.label, cloneNode);

            cloneNode.next = dfs(node.next, vis);
            if (node.random == node) {//有自环不要再往下搜索了，会死循环的！
                cloneNode.random = new RandomListNode(node.random.label);
            } else {
                cloneNode.random = dfs(node.random, vis);
            }

            return cloneNode;
        } else if (node == null) {
            return node;
        } else {
            //deal if the graph has a circle
            return vis.get(node.label);
        }

    }

    public RandomListNode copyRandomList(RandomListNode head) {
        if (head == null) return null;
        Map<Integer, RandomListNode> map = new HashMap<Integer, RandomListNode>();
        return dfs(head, map);
    }