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 Scala 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.scala
Replay: real traced execution (multi-file project)
class Node(val value: Int, var next: Node = null)

def render(head: Node): String = {
  val parts = scala.collection.mutable.ArrayBuffer[String]()
  var cursor = head
  while (cursor != null) {
    parts += cursor.value.toString
    cursor = cursor.next
  }
  parts.mkString(" -> ") + " -> null"
}

var head = new Node(10, new Node(20, new Node(30, new Node(40))))
val target = 30
var cursor = head
while (cursor.next != null) {
  if (cursor.next.value == target) {
    cursor.next = cursor.next.next
  }
  cursor = if (cursor.next == null) null else cursor.next
}
println(render(head))

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

    1class Node(val value: Int, var next: Node = null)
    values this step10 -> 20 -> 30 -> 40 -> nullhead30target

  2. cursor ← node(20)

    5var cursor = head6while (cursor != null) {7  parts += cursor.value.toString
    values this stepnode(10) → node(20)cursor

  3. cursor.next ← node(40)

    17if (cursor.next.value == target) {18  cursor.next = cursor.next.next19}
    values this stepnode(30) → node(40)cursor.next

  4. stdout ← 10 -> 20 -> 40 -> null

    21}22println(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.