copy-list-with-random-pointer.py

"""

A linked list of length n is given such that each node contains an additional random pointer, which could point to any node in the list, or null.

Construct a deep copy of the list. The deep copy should consist of exactly n brand new nodes, where each new node has its value set to the value of its corresponding original node. Both the next and random pointer of the new nodes should point to new nodes in the copied list such that the pointers in the original list and copied list represent the same list state. None of the pointers in the new list should point to nodes in the original list.

For example, if there are two nodes X and Y in the original list, where X.random --> Y, then for the corresponding two nodes x and y in the copied list, x.random --> y.

Return the head of the copied linked list.

The linked list is represented in the input/output as a list of n nodes. Each node is represented as a pair of [val, random_index] where:

val: an integer representing Node.val
random_index: the index of the node (range from 0 to n-1) that the random pointer points to, or null if it does not point to any node.
Your code will only be given the head of the original linked list.

 

Example 1:


Input: head = [[7,null],[13,0],[11,4],[10,2],[1,0]]
Output: [[7,null],[13,0],[11,4],[10,2],[1,0]]
Example 2:


Input: head = [[1,1],[2,1]]
Output: [[1,1],[2,1]]
Example 3:



Input: head = [[3,null],[3,0],[3,null]]
Output: [[3,null],[3,0],[3,null]]
Example 4:

Input: head = []
Output: []
Explanation: The given linked list is empty (null pointer), so return null.
 

Constraints:

0 <= n <= 1000
-10000 <= Node.val <= 10000
Node.random is null or is pointing to some node in the linked list.

"""

# V0
# IDEA : 
#   step 1) make 2 objects (m, n) refer to same instance (head)
#   step 2) go through m, and set up the dict
#   step 3) go through n, and get the random pointer via the dict we set up in step 2)
class Node(object):
    def __init__(self, val, next, random):
        self.val = val
        self.next = next
        self.random = random

class Solution:
    def copyRandomList(self, head):
        dic = dict()
        ### NOTE : make m, and n refer to same instance (head)
        m = n = head
        while m:
            ### NOTE : the value in dict is Node type (LinkedList)
            dic[m] = Node(m.val)
            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)

# V1
# https://blog.csdn.net/fuxuemingzhu/article/details/80787528
"""
# Definition for a Node.
class Node(object):
    def __init__(self, val, next, random):
        self.val = val
        self.next = next
        self.random = random
"""
class Solution(object):
    def copyRandomList(self, head):
        """
        :type head: Node
        :rtype: Node
        """
        nodeDict = dict()
        dummy = Node(0, None, None)
        nodeDict[head] = dummy
        newHead, pointer = dummy, head
        while pointer:
            node = Node(pointer.val, pointer.next, None)
            nodeDict[pointer] = node
            newHead.next = node
            newHead, pointer = newHead.next, pointer.next
        pointer = head
        while pointer:
            if pointer.random:
                nodeDict[pointer].random = nodeDict[pointer.random]
            pointer = pointer.next
        return dummy.next

### Test case : dev 

# V1'
# http://bookshadow.com/weblog/2015/07/31/leetcode-copy-list-random-pointer/
class Solution:
    # @param head, a RandomListNode
    # @return a RandomListNode
    def copyRandomList(self, head):
        nodeDict = dict()
        dummy = RandomListNode(0)
        pointer, newHead = head, dummy
        while pointer:
            newNode = RandomListNode(pointer.label)
            nodeDict[pointer] = newHead.next = newNode
            newHead, pointer = newHead.next, pointer.next
        pointer, newHead = head, dummy.next
        while pointer:
            if pointer.random:
                newHead.random = nodeDict[pointer.random]
            pointer, newHead = pointer.next, newHead.next
        return dummy.next

# V1''
# https://leetcode.com/problems/copy-list-with-random-pointer/discuss/43485/Clear-and-short-python-O(2n)-and-O(n)-solution
# Definition for a Node.
class Node(object):
    def __init__(self, val, next, random):
        self.val = val
        self.next = next
        self.random = random

class Solution:
    def copyRandomList(self, head):
        dic = dict()
        m = n = head
        while m:
            dic[m] = Node(m.val)
            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)

# V1'''
# https://leetcode.com/problems/copy-list-with-random-pointer/discuss/43485/Clear-and-short-python-O(2n)-and-O(n)-solution
class Node(object):
    def __init__(self, val, next, random):
        self.val = val
        self.next = next
        self.random = random
        
class Solution:
    def copyRandomList(self, head):
        dic = collections.defaultdict(lambda: Node(0))
        dic[None] = None
        n = head
        while n:
            dic[n].val = n.val
            dic[n].next = dic[n.next]
            dic[n].random = dic[n.random]
            n = n.next
        return dic[head]

# V1'''''
# https://www.jiuzhang.com/solution/copy-list-with-random-pointer/#tag-highlight-lang-python
class Solution:
    # @param head: A RandomListNode
    # @return: A RandomListNode
    def copyRandomList(self, head):
        # write your code here
        if head == None:
            return None
            
        myMap = {}
        nHead = RandomListNode(head.label)
        myMap[head] = nHead
        p = head
        q = nHead
        while p != None:
            q.random = p.random
            if p.next != None:
                q.next = RandomListNode(p.next.label)
                myMap[p.next] = q.next
            else:
                q.next = None
            p = p.next
            q = q.next
        
        p = nHead
        while p!= None:
            if p.random != None:
                p.random = myMap[p.random]
            p = p.next
        return nHead

# V2 
# Time:  O(n)
# Space: O(1)
class RandomListNode(object):
    def __init__(self, x):
        self.label = x
        self.next = None
        self.random = None

class Solution(object):
    # @param head, a RandomListNode
    # @return a RandomListNode
    def copyRandomList(self, head):
        # copy and combine copied list with original list
        current = head
        while current:
            copied = RandomListNode(current.label)
            copied.next = current.__next__
            current.next = copied
            current = copied.__next__

        # update random node in copied list
        current = head
        while current:
            if current.random:
                current.next.random = current.random.__next__
            current = current.next.__next__

        # split copied list from combined one
        dummy = RandomListNode(0)
        copied_current, current = dummy, head
        while current:
            copied_current.next = current.__next__
            current.next = current.next.__next__
            copied_current, current = copied_current.__next__, current.__next__
        return dummy.__next__

# V3 
# Time:  O(n)
# Space: O(n)
class Solution2(object):
    # @param head, a RandomListNode
    # @return a RandomListNode
    def copyRandomList(self, head):
        dummy = RandomListNode(0)
        current, prev, copies = head, dummy, {}
        while current:
            copied = RandomListNode(current.label)
            copies[current] = copied
            prev.next = copied
            prev, current = prev.__next__, current.__next__
        current = head
        while current:
            if current.random:
                copies[current].random = copies[current.random]
            current = current.__next__
        return dummy.__next__

# V4
# time: O(n)
# space: O(n)
from collections import defaultdict
class Solution3(object):
    def copyRandomList(self, head):
        """
        :type head: RandomListNode
        :rtype: RandomListNode
        """
        clone = defaultdict(lambda: RandomListNode(0))
        clone[None] = None
        cur = head

        while cur:
            clone[cur].label = cur.label
            clone[cur].next = clone[cur.__next__]
            clone[cur].random = clone[cur.random]
            cur = cur.__next__
        return clone[head]