Build a Singly Linked List

Construct a singly linked list by allocating one node per value and chaining next pointers. Establishes the node + head + tail model used by every later linked-list lesson.

Algorithm

Basic Implementation

basic.py

class Node:
    __slots__ = ("value", "next")
    def __init__(self, value):
        self.value = value
        self.next = None

values = [10, 20, 30, 40]
head = None
tail = None
for value in values:
    node = Node(value)
    if head is None:
        head = node
    else:
        tail.next = node
    tail = node

The canonical values [10, 20, 30, 40] become one node per value. The head pointer names the first node; the tail pointer names the last node appended.

Step 1 - First node

After appending 10, both head and tail point at the same node.

Step 2 - Append through 30

Each append changes the old tail's next pointer, then moves tail to the new node.

Step 3 - Final chain

Appending 40 gives the lesson's pinned chain: head -> 10 -> 20 -> 30 -> 40 -> null.

Complexity

Time: O(n) with a tail pointer
Space: O(n)

Implementation notes

Python: a small class with __slots__ = ("value", "next") is the idiomatic Node. A dataclass would work too.
The replay never shows object identity; nodes are labelled node(<value>) and the chain view is rendered as 1 -> 2 -> ... -> null.

node chain Each node carries a value and a `next` reference to the following node or `None`.