Datawhale | 編程第6期 Test 4

散列表（哈希表）

實現一個基於鏈表法解決衝突問題的散列表

class HashTable {
  constructor() {
    this.table = [];
  }

  loseHashCode(key) {
    let hash = 0;
    for (let i = 0; i < key.length; i++) {
      hash += key.charCodeAt(i);
    }

    return hash;
  }

  put(key, value) {
    const position = this.loseHashCode(key);
    if (this.table[position] == undefined) {
      this.table[position] = new LinkedList();
    }

    this.table[position].append(key, value);
  }

  get(key) {
    const position = this.loseHashCode(key);

    if (this.table[position] != undefined) {
      const current = this.table[position].getHead();

      while (current.next) {
        if (current.element.key === key) {
          return current.element.value;
        }

        current = current.next;
      }

      if (current.element.key === key) {
        return current.element.value;
      }

      return undefined;
    }

    return undefined;
  }

  remove(key) {
    const position = this.loseHashCode(key);

    if (this.table[position] !== undefined) {
      const current = this.table[position].getHead();

      do {
        if (current.element.key === key) {
          current.element.remove(key);

          if (this.table[position].isEmpty()) {
            this.table[position] = undefined;
          }

          return true;
        }

        current = current.next;
      } while (current);
    }

    return false;
  }

}

實現一個 LRU 緩存淘汰算法

class LRUCache {
  constructor(capacity) {
    this.capacity = capacity
    this.map = new Map()
  }

  get(key) {
    let val = this.map.get(key)
    if (typeof val === 'undefined') { return -1 }
    this.map.delete(key)
    this.map.set(key, val)
    return val
  }

  put(key, value) {
    if (this.map.has(key)) { 
      this.map.delete(key) 
    }

    this.map.set(key, value)
    let keys = this.map.keys()
    while (this.map.size > this.capacity) { this.map.delete(keys.next().value) }
  }
}

參考資料

• ES6 - map
• JavaScript 版數據結構與算法（六）散列表
• 解決哈希衝突的常用方法分析
• js算法入門（2）--哈希表