JavaScript 数据结构与算法 之 集合

集合

集合是由一组无序且唯一（即不能重复）的项组成

class Set {
  constructor() {
    this.items = {};
  }
  has(element) {
    return Object.prototype.hasOwnProperty.call(this.items, element);
  }
  add(element) {
    if (!this.has(element)) {
      this.items[element] = element;
      return true;
    }
    return false;
  }
  delete(element) {
    if (this.has(element)) {
      delete this.items[element];
      return true;
    }
    return false;
  }
  clear() {
    this.items = {};
  }
  size() { // 部分浏览器不支持
    return Object.keys(this.items).length;
  }
  sizeLegacy() {
    let count = 0;
    for (let key in this.items) {
      if (this.items.hasOwnProperty(key)) {
        count++;
      }
    }
    return count;
  }
  values() {
    return Object.values(this.items);
  }
  valuesLegacy() {
    let values = [];
    for (let key in this.items) {
      if (this.items.hasOwnProperty(key)) {
        values.push(key);
      }
    }
    return values;
  }

  union(otherSet) {
    const unionSet = new Set();
    this.values.forEach(value => unionSet.add(value));
    otherSet.forEach(value => unionSet.add(value));
    return unionSet;
  }

  intersection(otherSet) {
    const intersectionSet = new Set();
    const values = this.values();
    const otherValues = otherSet.values();
    let biggerSet = values;
    let smallerSet = otherValues;
    if (otherValues.length - values.length > 0) {
      biggerSet = otherValues;
      smallerSet = values;
    }
    smallerSet.forEach(value => {
      if (biggerSet.has(value)) {
        intersectionSet.add(value);
      }
    });
    return intersectionSet;
  }

  difference(otherSet) {
    const differenceSet = new Set();
    this.values.forEach(value => {
      if (!otherSet.has(value)) {
        differenceSet.add(value);
      }
    });
    return differenceSet;
  }
  
  isSubsetOf(otherSet) {
    if (this.size() > otherSet.size()) {
      return false;
    }
    let isSubset = true;
    this.values().every(value => {
      if (!otherSet.has(value)) {
        isSubset = false;
        return false;
      }
      return true;
    });
    return isSubset;
  }
}