Python/data_structures/linked_list/singly_linked_list.py
Christian Clauss 0e6e5056b3
singly_linked_list.py: psf/black (#2008)
* singly_linked_list.py: psf/black

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* Update singly_linked_list.py

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2020-05-19 13:54:25 +02:00

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Python

class Node:
def __init__(self, data):
self.data = data
self.next = None
def __repr__(self):
return f"Node({self.data})"
class LinkedList:
def __init__(self):
self.head = None # initialize head to None
def insert_tail(self, data) -> None:
if self.head is None:
self.insert_head(data) # if this is first node, call insert_head
else:
temp = self.head
while temp.next: # traverse to last node
temp = temp.next
temp.next = Node(data) # create node & link to tail
def insert_head(self, data) -> None:
new_node = Node(data) # create a new node
if self.head:
new_node.next = self.head # link new_node to head
self.head = new_node # make NewNode as head
def print_list(self) -> None: # print every node data
temp = self.head
while temp:
print(temp.data)
temp = temp.next
def delete_head(self): # delete from head
temp = self.head
if self.head:
self.head = self.head.next
temp.next = None
return temp
def delete_tail(self): # delete from tail
temp = self.head
if self.head:
if self.head.next is None: # if head is the only Node in the Linked List
self.head = None
else:
while temp.next.next: # find the 2nd last element
temp = temp.next
# (2nd last element).next = None and temp = last element
temp.next, temp = None, temp.next
return temp
def is_empty(self) -> bool:
return self.head is None # return True if head is none
def reverse(self):
prev = None
current = self.head
while current:
# Store the current node's next node.
next_node = current.next
# Make the current node's next point backwards
current.next = prev
# Make the previous node be the current node
prev = current
# Make the current node the next node (to progress iteration)
current = next_node
# Return prev in order to put the head at the end
self.head = prev
def __repr__(self): # String representation/visualization of a Linked Lists
current = self.head
string_repr = ""
while current:
string_repr += f"{current} --> "
current = current.next
# END represents end of the LinkedList
return string_repr + "END"
# Indexing Support. Used to get a node at particular position
def __getitem__(self, index):
current = self.head
# If LinkedList is empty
if current is None:
raise IndexError("The Linked List is empty")
# Move Forward 'index' times
for _ in range(index):
# If the LinkedList ends before reaching specified node
if current.next is None:
raise IndexError("Index out of range.")
current = current.next
return current
# Used to change the data of a particular node
def __setitem__(self, index, data):
current = self.head
# If list is empty
if current is None:
raise IndexError("The Linked List is empty")
for i in range(index):
if current.next is None:
raise IndexError("Index out of range.")
current = current.next
current.data = data
def __len__(self):
"""
Return length of linked list i.e. number of nodes
>>> linked_list = LinkedList()
>>> len(linked_list)
0
>>> linked_list.insert_tail("head")
>>> len(linked_list)
1
>>> linked_list.insert_head("head")
>>> len(linked_list)
2
>>> _ = linked_list.delete_tail()
>>> len(linked_list)
1
>>> _ = linked_list.delete_head()
>>> len(linked_list)
0
"""
if not self.head:
return 0
count = 0
cur_node = self.head
while cur_node.next:
count += 1
cur_node = cur_node.next
return count + 1
def main():
A = LinkedList()
A.insert_head(input("Inserting 1st at head ").strip())
A.insert_head(input("Inserting 2nd at head ").strip())
print("\nPrint list:")
A.print_list()
A.insert_tail(input("\nInserting 1st at tail ").strip())
A.insert_tail(input("Inserting 2nd at tail ").strip())
print("\nPrint list:")
A.print_list()
print("\nDelete head")
A.delete_head()
print("Delete tail")
A.delete_tail()
print("\nPrint list:")
A.print_list()
print("\nReverse linked list")
A.reverse()
print("\nPrint list:")
A.print_list()
print("\nString representation of linked list:")
print(A)
print("\nReading/changing Node data using indexing:")
print(f"Element at Position 1: {A[1]}")
A[1] = input("Enter New Value: ").strip()
print("New list:")
print(A)
print(f"length of A is : {len(A)}")
if __name__ == "__main__":
main()