集合

• 集合是一组无序且唯一的项组成。

class Set{
  constructor() {
    this.items = {}
  }
  has(element) {
    // return element in this.items
    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 items[element]
      return true
    }
    return false
  }
  clear() {
    this.items = {}
  }
  size() {
    return Object.keys(this.items).length
  }
  value() {
    return Object.values(this.items)
  }
  //并集
  union(otherSet) {
    const unionSet = new Set()
    this.values().forEach(value => unionSet.add(value))
    otherSet.values().forEach(value => unionSet.add(value))
    return unionSet
  }
  //交集
  intersection(otherSet) {
    //1.第一种写法
    // const intersectionSet = new Set()
    // const values = this.values()
    // for (let i = 0; i < values.length; i++){
    //   if (otherSet.has(values[i])) {
    //     intersectionSet.add(values[i])
    //   }
    // }
    // return intersectionSet
    //第二种写法
    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(values => {
      if (biggerSet.includes(values)) {
        intersectionSet.add(values)
      }
    })
    return intersectionSet
  }
  //差集
  difference(otherSet) {
    const differenceSet = new Set()
    this.values().forEach(value => {
      if (!otherSet.has(value)) {
        differenceSet.add(value)
      }
    })
    return differenceSet
  }
  //子集
  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
  }
}