集合的特点
1.无序
2.唯一性
3.不可重复

集合相对于前面几种数据结构，比较简单好理解，看看代码实现就能知道他的用法了

集合的创建

function MySet() {
  this.item = {};
}
MySet.prototype.has = function (value) {
  return value in this.item;
};

//增
MySet.prototype.add = function (value) {
  if (this.has(value)) return false;
  this.item[value] = value;
  return true;
};

//删
MySet.prototype.remove = function (value) {
  if (!this.has(value)) return false;
  delete this.item[value];
  return true;
};

//清空
MySet.prototype.clear = function () {
  this.item = {};
};

//长度
MySet.prototype.size = function () {
  return Object.keys(this.item).length;
};

//获取值
MySet.prototype.values = function () {
  let arr = [];
  console.log("🚀 ~ Object.keys(this.item):", Object.keys(this.item));
  for (i = 0; i < Object.keys(this.item).length; i++) {
    const key = Object.keys(this.item)[i];
    arr.push(this.item[key]);
  }
  return arr;
};

//查询
MySet.prototype.print = function () {
  console.log(this.item);
  return this.item;
};

//集合的操作

//求并集
MySet.prototype.addUnion = function (data) {
  let newSet = new MySet();

  let values = this.values();

  for (let i = 0; i < values.length; i++) {
    newSet.add(values[i]);
  }

  let values2 = data.values();
  for (let i = 0; i < values2.length; i++) {
    newSet.add(values2[i]);
  }
  return newSet.values();
};

//求交集

MySet.prototype.interSection = function (data) {
  const interSection = new MySet();

  const oldValues = this.values();
  for (let i = 0; i < oldValues.length; i++) {
    if (data.has(oldValues[i])) {
      interSection.add(oldValues[i]);
    }
  }
  return interSection.values();
};

//求差集

MySet.prototype.diff = function (data) {
  const diff = new MySet();

  const oldValues = this.values();
  for (let i = 0; i < oldValues.length; i++) {
    if (!data.has(oldValues[i])) {
      diff.add(oldValues[i]);
    }
  }
  return diff.values();
};

测试

const set = new MySet()
      set.add('a',1)
      set.add('b',2)

      console.log(set.print())
      console.log('values',set.values())



      //测试求并集
      const set1 = new MySet()
      set1.add(1)
      set1.add(2)
      set1.add(3)

      const set2 = new MySet()
      set2.add(3)
      set2.add(4)
      set2.add(5)
      set2.add(6)
      set2.add(7)

      const result = set1.addUnion(set2)
      console.log(result)  //[1, 2, 3, 4, 5, 6, 7]


      //求交集
      const set3 = new MySet()
      set3.add(1)
      set3.add(2)
      set3.add(3)

      const set4 = new MySet()
      set4.add(3)
      set4.add(4)
      set4.add(5)
      set4.add(6)

      const result2 = set3.interSection(set4)
      console.log("🚀 ~ result2:", result2)

      //求差集
      const set5 = new MySet()
      set5.add(1)
      set5.add(2)
      set5.add(3)

      const set6 = new MySet()

      set6.add(3)
      set6.add(4)

      const result3 = set5.diff(set6)
      console.log("🚀 ~ result3:", result3)

可以参照着练习下，其实不难，这个知识点！！