Linked Structures

Traverse and Print

Walk from the head pointer to null, visiting each node exactly once without random indexing.

Algorithm

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

cursor A cursor reference names the node currently being visited.
null stop Traversal ends when the cursor reaches the null marker.

Basic Implementation

basic.swift
Replay: real traced execution (multi-file project)
final class Node {
    let value: Int
    var next: Node?
    init(_ value: Int, _ next: Node? = nil) {
        self.value = value
        self.next = next
    }
}

func render(_ head: Node?) -> String {
    var parts: [String] = []
    var cursor = head
    while cursor != nil {
        parts.append(String(cursor!.value))
        cursor = cursor!.next
    }
    return parts.joined(separator: " -> ") + " -> null"
}

var head: Node? = Node(10, Node(20, Node(30)))
print(render(head))

  1. head ← 10 -> 20 -> 30 -> null

    1final class Node {2    let value: Int
    values this step10 -> 20 -> 30 -> nullhead

  2. output ← 10

    12var cursor = head13while cursor != nil {14    parts.append(String(cursor!.value))
    values this step10outputnode(10)cursor

  3. output ← 10 -> 20

    12var cursor = head13while cursor != nil {14    parts.append(String(cursor!.value))
    values this step10 -> 20outputnode(20)cursor

  4. output ← 10 -> 20 -> 30 -> null

    12var cursor = head13while cursor != nil {14    parts.append(String(cursor!.value))
    values this step10 -> 20 -> 30 -> nulloutputnode(30)cursor

  5. stdout ← 10 -> 20 -> 30 -> null

    20var head: Node? = Node(10, Node(20, Node(30)))21print(render(head))
    values this step10 -> 20 -> 30 -> nullstdout10 -> 20 -> 30 -> nulloutput

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.