# Stack

A specific implementation of a singly linked list where you only add or remove from the head. (first in last out)

Implemented very similarly to a queue.

type Node<T> = {
  value: T;
  prev?: Node<T>;
};

class Stack<T> {
  public length: number;
  private head?: Node<T>;

  constructor() {
    this.head = undefined;
    this.length = 0;
  }

  push(item: T): void {
    const node = { value: item } as Node<T>;

    this.length++;

    if (!this.head) {
      this.head = node;
      return;
    }

    node.prev = this.head;
    this.head = node;
  }

  pop(): T | undefined {
    this.length = Math.max(0, this.length - 1);
    const head = this.head!;

    if (this.length === 0) {
      this.head = undefined;
      return head?.value;
    }

    this.head = head.prev;

    // free
    head.prev = undefined;

    return head.value;
  }

  peek(): T | undefined {
    return this.head?.value;
  }
}