leetcode 138

class Solution(object):
    def copyRandomList(self, head):
        if head == None: return None
        map_to_copy = {}
        node = head
        while node != None:
            node_copy = RandomListNode(node.label)
            map_to_copy[node] = node_copy
            node = node.next
            
        node = head
        while node != None:
            node_copy = map_to_copy[node]
            if node.next: node_copy.next = map_to_copy[node.next]
            if node.random: node_copy.random = map_to_copy[node.random]
            node = node.next
            
        return map_to_copy[head]