DSA 34: LinkedList - Read & Search [Part 2]

1. Node and LinkedList

Introduced previously.

class Node():
    def __init__(self, data):
        self.data=data
        self.next_node=None
        
node0=Node("I")
node1=Node("heard")
node2=Node("there")
node3=Node("was")

node0.next_node=node1
node1.next_node=node2
node2.next_node=node3

class LinkedList():
    def __init__(self, first_node: Node):
        self.first_node=first_node

ll = LinkedList(first_node=node0)

2. Type-Annotations

I started using Type-Annotations (E.g. linked_list: LinkedList) in my function arguments:

• because when I typed something like current_node. (an instance with a . attribute-accessor), then,
• I will be presented with current_node’s attributes to choose from in Visual Studio Code (VSC).
• This is because of the linting by Pylance extension that comes with VSC.

Notice data and next_node are at the top of the list.

3. LinkedList: Read() at Index & Return Node.data

def read_ll_tp1(linked_list: LinkedList, idx: int) -> str | None:
    current_node = linked_list.first_node
    for i in range(idx):
        # print(i)
        current_node = current_node.next_node
        if not current_node:
            # raise IndexError("LinkedList exhausted!")
            return None
    return current_node.data

print(read_ll_tp1(ll,0))
print(read_ll_tp1(ll,1))
print(read_ll_tp1(ll,2))
print(read_ll_tp1(ll,3))
print(read_ll_tp1(ll,4))

I
heard
there
was
None

4. LinkedList: Search() for Value & Return Index

def search_ll_tp1(linked_list: LinkedList, value: str) -> int | None:
    current_node = linked_list.first_node
    i=0
    while current_node:
        if current_node.data == value:
            return i
        current_node = current_node.next_node
        # if not current_node: <- redundant since inside while current_node
        #     return None 
        i+=1
    return None # <- if current_node is false return None

print(search_ll_tp1(ll,"I"))
print(search_ll_tp1(ll,"heard"))
print(search_ll_tp1(ll,"there"))
print(search_ll_tp1(ll,"was"))
print(search_ll_tp1(ll,"a"))

0
1
2
3
None