Lru cache

LRU cache 其實很好理解，就是邊緣人理論

一個 node 如果被不理很久（write or read），那位子滿了就自然要把這個邊緣人 node 趕出去，

這世界就是這麼現實ＱＱ

Requirement

READ O(1)

WRITE O(1)

Map

Linked List

reduce time, increase capcity

Implement LRU Cache

codehike demo

class LRUCacheNode {
  key: string;
  value: any;
  next: LRUCacheNode | null;
  prev: LRUCacheNode | null;

  constructor(
    key: string,
    value: string,
    next: LRUCacheNode | null = null,
    prev: LRUCacheNode | null = null
  ) {
    this.key = key;
    this.value = value;
    this.next = next;
    this.prev = prev;
  }
}

export class LRUCache {
  size: number;
  limit: number;
  head: LRUCacheNode | null;
  tail: LRUCacheNode | null;
  cacheMap: Record<string, LRUCacheNode>;

  constructor(limit = 10) {
    this.size = 0;
    this.limit = limit;
    this.head = null;
    this.tail = null;
    this.cacheMap = {};
  }

  private detach(node: LRUCacheNode) {
    if (node.prev instanceof LRUCacheNode) {
      node.prev.next = node.next;
    } else {
      this.head = node.next;
    }

    if (node.next instanceof LRUCacheNode) {
      node.next.prev = node.prev;
    } else {
      this.tail = node.prev;
    }
  }

  public write(key: string, value: string) {
    const existingNode = this.cacheMap[key];

    if (existingNode) {
      this.detach(existingNode);
      this.size--;
    } else if (this.size === this.limit && this.tail) {
      delete this.cacheMap[this.tail.key];
      this.detach(this.tail);
      this.size--;
    }

    if (!this.head) {
      this.head = this.tail = new LRUCacheNode(key, value);
    } else {
      const node = new LRUCacheNode(key, value, this.head);
      this.head.prev = node;
      this.head = node;
    }

    this.cacheMap[key] = this.head;
    this.size++;
  }

  public read(key: string) {
    const existingNode = this.cacheMap[key];

    if (existingNode) {
      const value = existingNode.value;

      if (this.head !== existingNode) {
        this.write(key, value);
      }

      return value;
    } else {
      console.log(`Item not vailable in cache for key ${key}`);
    }
  }

  public clear() {
    this.head = null;
    this.tail = null;
    this.size = 0;
    this.cacheMap = {};
  }
}

If consecutive cache his(2 or more time) are count as being used

export class LRUCache {
  size: number;
  limit: number;
  head: LRUCacheNode | null;
  tail: LRUCacheNode | null;
  cacheMap: Record<string, LRUCacheNode>;

  constructor(limit = 10) {
    this.size = 0;
    this.limit = limit;
    this.head = null;
    this.tail = null;
    this.cacheMap = {};
  }

  private detach(node: LRUCacheNode) {
    if (node.prev instanceof LRUCacheNode) {
      node.prev.next = node.next;
    } else {
      this.head = node.next;
    }

    if (node.next instanceof LRUCacheNode) {
      node.next.prev = node.prev;
    } else {
      this.tail = node.prev;
    }
  }

  public write(key: string, value: string) {
    const existingNode = this.cacheMap[key];
    
    /** If the hit is less than twice, the linked-list will not be changed */
    if (existingNode && existingNode.hits < 1) {
      existingNode.value = value;
      existingNode.hits++;
      return;
    }

    if (existingNode) {
      this.detach(existingNode);
      this.size--;
    } else if (this.size === this.limit && this.tail) {
      delete this.cacheMap[this.tail.key];
      this.detach(this.tail);
      this.size--;
    }

    if (!this.head) {
      this.head = this.tail = new LRUCacheNode(key, value);
    } else {
      const node = new LRUCacheNode(key, value, this.head);
      this.head.prev = node;
      this.head = node;
    }

    this.cacheMap[key] = this.head;
    this.size++;
  }

  public read(key: string) {
    const existingNode = this.cacheMap[key];

    if (existingNode) {
      const value = existingNode.value;

      if (this.head !== existingNode) {
        this.write(key, value);
      }

      return value;
    } else {
      console.log(`Item not vailable in cache for key ${key}`);
    }
  }

  public clear() {
    this.head = null;
    this.tail = null;
    this.size = 0;
    this.cacheMap = {};
  }
}

LRU Cache

By Jay Chou

Lru cache

Requirement

Implement LRU Cache

LRU Cache

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