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Build the reversed list by iterating through the given linked list from first to last and prepending every node to the reversed list, pointing each node’s next pointer to the previously added node.
Has anyone done this challenge using recursion? (I did not.)
I added in checking if each node had a next attribute, otherwise I kept getting an error.
My solution is longer than the ones in the other posts.
My solution to the challenge
def reverse_linked_list(linked_list):
current_node = linked_list
if linked_list is None:
return None
if not hasattr(current_node, "next"):
return Node(current_node.data)
next_node = current_node.next
reversed_node_list = []
reversed_node = Node(current_node.data)
reversed_node_list.append(reversed_node)
while next_node is not None:
reversed_node = Node(next_node.data, reversed_node)
reversed_node_list.insert(0, reversed_node)
current_node = next_node
if not hasattr(current_node, "next"):
break
next_node = current_node.next
return reversed_node
Here’s proof that it works:
class Node:
def __init__(self, data, next_node=None):
self.data = data
self.next = next_node
def __repr__(self):
data = str(self.data)
if self.next is None:
return data + " -> None"
elif hasattr(self.next, "data"):
return data + " -> " + str(node.next.data)
else:
return data + " -> " + repr(node.next)
def print_linked_list(self):
print(self.data)
current = self
next = current.next
while next is not None:
print(next.data)
current = next
next = current.next
def make_linked_list(list_of_data):
node_list = []
current = None
previous = None
for item in list_of_data:
current = Node(item)
node_list.append(current)
if previous is not None:
previous.next = current
previous = current
if len(node_list) == 0:
return None
else:
return node_list[0]
def reverse_linked_list(linked_list):
current_node = linked_list
if linked_list is None:
return None
if not hasattr(current_node, "next"):
return Node(current_node.data)
next_node = current_node.next
reversed_node_list = []
reversed_node = Node(current_node.data)
reversed_node_list.append(reversed_node)
while next_node is not None:
reversed_node = Node(next_node.data, reversed_node)
reversed_node_list.insert(0, reversed_node)
current_node = next_node
if not hasattr(current_node, "next"):
break
next_node = current_node.next
return reversed_node
def print_linked_list(head_node, between = " -> "):
print(head_node.data, end = between )
current = head_node
next = current.next
while next is not None:
print(next.data, end = between )
current = next
next = current.next
print("None")
def data_iterator(head_node):
# generator function
current = head_node
yield current.data
while hasattr(current, "next") and current.next is not None:
current = current.next
yield current.data
print("Original")
demo_list = make_linked_list([4,8,15])
print_linked_list(demo_list)
print("Reversed")
reverse = reverse_linked_list(demo_list)
print_linked_list(reverse)
#print(list(data_iterator(reverse)))
print("Original Unchanged")
print_linked_list(demo_list)
) below.
) to up-vote the contribution!