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Python Linked List: Print a given doubly linked list in reverse order

Python Linked List: Exercise-11 with Solution

Write a Python program to print a given doubly linked list in reverse order.

Sample Solution:-

Python Code:

class Node(object):
    # Singly linked node
    def __init__(self, data=None, next=None, prev=None):
        self.data = data
        self.next = next
        self.prev = prev

class doubly_linked_list(object):
    def __init__(self):
        self.head = None
        self.tail = None
        self.count = 0

    def append_item(self, data):
        # Append an item 
        new_item = Node(data, None, None)
        if self.head is None:
            self.head = new_item
            self.tail = self.head
        else:
            new_item.prev = self.tail
            self.tail.next = new_item
            self.tail = new_item
        self.count += 1
    
    def iter(self):
        # Iterate the list
        current = self.head
        while current:
            item_val = current.data
            current = current.next
            yield item_val

    def print_foward(self):
        for node in self.iter():
            print(node)   
        
    def reverse(self):
        """ Reverse linked list. """
        current = self.head
        while current:
            temp = current.next
            current.next = current.prev
            current.prev = temp
            current = current.prev
        temp = self.head
        self.head = self.tail
        self.tail = temp

items = doubly_linked_list()
items.append_item('PHP')
items.append_item('Python')
items.append_item('C#')
items.append_item('C++')
items.append_item('Java')
items.append_item('SQL')

print("Reverse list ")
items.reverse()
items.print_foward()

Sample Output:

Reverse list 
SQL
Java
C++
C#
Python
PHP

Flowchart:

Flowchart: Print a given doubly linked list in reverse order.

Python Code Editor:

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Previous: Write a Python program to count the number of items of a given doubly linked list.
Next: Write a Python program to insert an item in front of a given doubly linked list.

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Python: Tips of the Day

Creates a dictionary with the same keys as the provided dictionary and values generated by running the provided function for each value:

Example:

def tips_map_values(obj, fn):
  ret = {}
  for key in obj.keys():
    ret[key] = fn(obj[key])
  return ret
users = {
  'Owen': { 'user': 'Owen', 'age': 29 },
  'Eddie': { 'user': 'Eddie', 'age': 15 }
}

print(tips_map_values(users, lambda u : u['age'])) # {'Owen': 29, 'Eddie': 15}

Output:

{'Owen': 29, 'Eddie': 15}