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 Lua 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.lua
Replay: real traced execution (multi-file project)
local function node(value, next)
    return { value = value, next = next }
end

local function render(head)
    local parts = {}
    local cursor = head
    while cursor ~= nil do
        parts[#parts + 1] = tostring(cursor.value)
        cursor = cursor.next
    end
    return table.concat(parts, " -> ") .. " -> null"
end

local head = node(10, node(20, node(30, node(40, nil))))
local target = 30
local cursor = head
while cursor.next ~= nil do
    if cursor.next.value == target then
        cursor.next = cursor.next.next
        break
    end
    cursor = cursor.next
end
print(render(head))

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

    1local function node(value, next)2    return { value = value, next = next }
    values this step10 -> 20 -> 30 -> 40 -> nullhead30target

  2. cursor ← node(20)

    7local cursor = head8while cursor ~= nil do9    parts[#parts + 1] = tostring(cursor.value)
    values this stepnode(10) → node(20)cursor

  3. cursor.next ← node(40)

    19if cursor.next.value == target then20    cursor.next = cursor.next.next21    break
    values this stepnode(30) → node(40)cursor.next

  4. stdout ← 10 -> 20 -> 40 -> null

    24end25print(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.