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);
}