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Basics

Design​

707. Design Linked List​

Medium·
Solutions:
tip

The playground replays a scripted sequence of MyLinkedList operations and steps through each method on the linked list. Use the operations editor to change the constructor args or the method sequence.

FIG. DESIGN LINKED LIST● INTERACTIVE
Visualize
class SinglyLLNode:
def __init__(self, val: Any, next=None):
self.val = val
self.next = next
 
 
class MyLinkedList:
def __init__(self):
self.sentinel = SinglyLLNode(None, None)
self.len = 0
 
def get(self, index: int) -> int:
node = self.goToIndex(index)
return node.val if node else -1
 
def addAtHead(self, val: int) -> None:
new_node = SinglyLLNode(val)
new_node.next = self.sentinel.next
self.sentinel.next = new_node
self.len += 1
 
def addAtTail(self, val: int) -> None:
new_node = SinglyLLNode(val)
current_node = self.sentinel
while current_node.next:
current_node = current_node.next
current_node.next = new_node
self.len += 1
 
def addAtIndex(self, index: int, val: int) -> None:
prev_node = self.goToIndex(index - 1)
if prev_node:
new_node = SinglyLLNode(val)
new_node.next = prev_node.next
prev_node.next = new_node
self.len += 1
 
def goToIndex(self, index: int) -> Optional[SinglyLLNode]:
current_index = -1
current_node = self.sentinel
while current_node.next and current_index < index:
current_node = current_node.next
current_index += 1
if current_index == index:
return current_node
return None
 
def deleteAtIndex(self, index: int) -> None:
prev_node = self.goToIndex(index - 1)
if prev_node and prev_node.next:
prev_node.next = prev_node.next.next
self.len -= 1

Reusable Code​

Count Linked List Nodes​

Basic·
Solutions:
FIG. COUNT LINKED LIST NODES● INTERACTIVE
Visualize
def getLen(head):
length = 0
while head:
head = head.next
length += 1
return length