LRU Cache with Map and Linked List

index.ts

class ListNode<T> {
  next: ListNode<T> | null = null;
  constructor(readonly data: T) {}
}

class LinkedList {
  private size: number = 0;
  private head: ListNode<string> | null = null;

  get(data: string): null | unknown {
    if (!this.head) {
      return null;
    }
    let current: ListNode<string> | null = this.head;
    while (current) {
      if (current.data === data) {
        return data;
      }
      current = current.next;
    }
    return null;
  }

  unshift(data: string) {
    const node = new ListNode(data);
    this.size++;
    if (!this.head) {
      this.head = node;
      return;
    }

    node.next = this.head;
    this.head = node;
  }

  remove(data: string): boolean {
    if (!this.head) {
      return false;
    }
    if (this.head.data === data) {
      this.head = this.head.next;
      this.size--;
      return true;
    }
    let current = this.head.next;
    let previous = this.head;
    while (current) {
      if (current.data === data) {
        previous.next = current.next;
        this.size--;
        return true;
      }
      previous = current;
      current = current.next;
    }

    return false;
  }

  pop(): string | null {
    if (!this.head) {
      return null;
    }
    if (!this.head.next) {
      // If only one node in the list
      let temp = this.head.data;
      this.head = null;
      this.size--;
      return temp;
    }
    let current = this.head;
    while (current.next && current.next.next) {
      current = current.next;
    }
    // Current is now the penultimate
    let temp = current.next!.data;
    current.next = null;
    this.size--;
    return temp;
  }
}

// LRU Cache
class LRUCache {
  private cache: Map<string, unknown>;
  lru: LinkedList;
  constructor(readonly capacity: number) {
    this.cache = new Map<string, unknown>();
    this.lru = new LinkedList();
  }

  get(key: string): any {
    const value = this.cache.get(key);
    if (!value) return null;

    // Add to the top of the Set
    this.lru.remove(key);
    this.lru.unshift(key);

    return value;
  }

  set(key: string, val: unknown) {
    // If full capacity, removed the Least Recently Used
    if (this.cache.size === this.capacity) {
      const removed = this.lru.pop();
      if (removed) {
        this.cache.delete(removed);
      }
    }
    this.lru.unshift(key);
    this.cache.set(key, val);
  }
}