Build a Singly Linked List

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

Algorithm

Canonical input [10, 20, 30, 40] builds the chain head -> 10 -> 20 -> 30 -> 40 -> null with one node appended per step.

Basic Implementation

basic.ts

class ListNode {
    value: number;
    next: ListNode | null;
    constructor(value: number) {
        this.value = value;
        this.next = null;
    }
}

const values: number[] = [10, 20, 30, 40];
let head: ListNode | null = null;
let tail: ListNode | null = null;
for (const v of values) {
    const node: ListNode = new ListNode(v);
    if (head === null) {
        head = node;
    } else {
        tail!.next = node;
    }
    tail = node;
}

Complexity

Time: O(n) with a tail pointer
Space: O(n) for the chain

Implementation notes

TypeScript: a small class ListNode with explicit field types is the idiomatic Node. The ListNode | null union types head, tail, and next honestly.
The replay never shows runtime references; nodes are labelled node(<value>) and the chain view is rendered as 10 -> 20 -> ... -> null.

node chain Each `ListNode` carries a `value: number` and a `next: ListNode | null` reference.