关于javascript:javascript-数据结构系列-六-哈希表

明天持续数据结构系列 哈希表 hash-table, 看一代码实现
构造函数如下

  /**
   * @param {number} hashTableSize
   */
  constructor(hashTableSize = defaultHashTableSize) {
    // Create hash table of certain size and fill each bucket with empty linked list.
    this.buckets = Array(hashTableSize).fill(null).map(() => new LinkedList());

    // Just to keep track of all actual keys in a fast way.
    this.keys = {};}

hash 办法

  /**
   * Converts key string to hash number.
   *
   * @param {string} key
   * @return {number}
   */
  hash(key) {
    // For simplicity reasons we will just use character codes sum of all characters of the key
    // to calculate the hash.
    //
    // But you may also use more sophisticated approaches like polynomial string hash to reduce the
    // number of collisions:
    //
    // hash = charCodeAt(0) * PRIME^(n-1) + charCodeAt(1) * PRIME^(n-2) + ... + charCodeAt(n-1)
    //
    // where charCodeAt(i) is the i-th character code of the key, n is the length of the key and
    // PRIME is just any prime number like 31.
    const hash = Array.from(key).reduce((hashAccumulator, keySymbol) => (hashAccumulator + keySymbol.charCodeAt(0)),
      0,
    );

    // Reduce hash number so it would fit hash table size.
    return hash % this.buckets.length;
  }

set 办法

  /**
   * @param {string} key
   * @param {*} value
   */
  set(key, value) {const keyHash = this.hash(key);
    this.keys[key] = keyHash;
    const bucketLinkedList = this.buckets[keyHash];
    const node = bucketLinkedList.find({callback: (nodeValue) => nodeValue.key === key });

    if (!node) {
      // Insert new node.
      bucketLinkedList.append({key, value});
    } else {
      // Update value of existing node.
      node.value.value = value;
    }
  }

delete 办法

  /**
   * @param {string} key
   * @return {*}
   */
  delete(key) {const keyHash = this.hash(key);
    delete this.keys[key];
    const bucketLinkedList = this.buckets[keyHash];
    const node = bucketLinkedList.find({callback: (nodeValue) => nodeValue.key === key });

    if (node) {return bucketLinkedList.delete(node.value);
    }

    return null;
  }

get 办法

  /**
   * @param {string} key
   * @return {*}
   */
  get(key) {const bucketLinkedList = this.buckets[this.hash(key)];
    const node = bucketLinkedList.find({callback: (nodeValue) => nodeValue.key === key });

    return node ? node.value.value : undefined;
  }

has 办法

  /**
   * @param {string} key
   * @return {boolean}
   */
  has(key) {return Object.hasOwnProperty.call(this.keys, key);
  }

getKeys 办法

  /**
   * @return {string[]}
   */
  getKeys() {return Object.keys(this.keys);
  }

至此，曾经实现了一个简略 hash-table!!!