copy_random_pointer.py

"""
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.
"""

class Solution:
# @param head, a RandomListNode
# @return a RandomListNode
def copyRandomList(self, head):
    dic = dict()
    m = n = head
    while m:
        dic[m] = RandomListNode(m.label)
        m = m.next
    while n:
        dic[n].next = dic.get(n.next)
        dic[n].random = dic.get(n.random)
        n = n.next
    return dic.get(head)

#O(n)
class Solution:
# @param head, a RandomListNode
# @return a RandomListNode
def copyRandomList(self, head):
    copy = collections.defaultdict(lambda: RandomListNode(0))
    copy[None] = None
    node = head
    while node:
        copy[node].label = node.label
        copy[node].next = copy[node.next]
        copy[node].random = copy[node.random]
        node = node.next
    return copy[head]