Linked Structures

Delete by Value

Find the node before the target value and rewire its next pointer so the target node leaves the chain.

Algorithm

The replay labels nodes by value, such as node(20), and never exposes object identity or memory addresses. This Python DSA implementation uses the same small chain as the rest of the DSA track.

predecessor Deletion needs the node before the one being removed.
rewiring The predecessor skips the target and points at the target's next node.

Basic Implementation

basic.py
Replay: real traced execution (multi-file project)
class Node:
    __slots__ = ("value", "next")
    def __init__(self, value, nxt=None):
        self.value = value
        self.next = nxt

def render(head):
    parts = []
    cursor = head
    while cursor is not None:
        parts.append(str(cursor.value))
        cursor = cursor.next
    return " -> ".join(parts) + " -> null"

head = Node(10, Node(20, Node(30, Node(40))))
target = 30
cursor = head
while cursor.next is not None:
    if cursor.next.value == target:
        cursor.next = cursor.next.next
        break
    cursor = cursor.next
print(render(head))

  1. head ← 10 -> 20 -> 30 -> 40 -> null, target ← 30

    1class Node:2    __slots__ = ("value", "next")
    values this step10 -> 20 -> 30 -> 40 -> nullhead30target

  2. cursor ← node(20)

    9cursor = head10while cursor is not None:11    parts.append(str(cursor.value))
    values this stepnode(10) → node(20)cursor

  3. cursor.next ← node(40)

    19if cursor.next.value == target:20    cursor.next = cursor.next.next21    break
    values this stepnode(30) → node(40)cursor.next

  4. stdout ← 10 -> 20 -> 40 -> null

    22    cursor = cursor.next23print(render(head))
    values this step10 -> 20 -> 40 -> nullstdout10 -> 20 -> 40 -> nullhead

Complexity

  • Time: O(n)
  • Space: O(1)

Implementation notes

  • Keep the explicit node and pointer/reference operations; array shortcuts hide the linked-list state this lesson is meant to replay.
  • The final output prints the chain in a deterministic a -> b -> null form for cross-language comparison.