XSet.js

class XSet extends Set {     
  union(...sets) {        
  return XSet.union(this, ...sets)      
}      
intersection(...sets) {        
  return XSet.intersection(this, ...sets);      
}      
difference(set) {        
  return XSet.difference(this, set);      
}      
symmetricDifference(set) {        
  return XSet.symmetricDifference(this, set);      
}      
cartesianProduct(set) {        
  return XSet.cartesianProduct(this, set);      
}      
powerSet() {        
  return XSet.powerSet(this);      
}    
  // 返回两个或更多集合的并集    static union(a, ...bSets) {      const unionSet = new XSet(a);      for (const b of bSets) {        for (const bValue of b) {          unionSet.add(bValue);        }      }      return unionSet;    }    // 返回两个或更多集合的交集    static intersection(a, ...bSets) {      const intersectionSet = new XSet(a);      for (const aValue of intersectionSet) {        for (const b of bSets) {          if (! b.has(aValue)) {            intersectionSet.delete(aValue);          }        }      }      return intersectionSet;    }    // 返回两个集合的差集    static difference(a, b) {      const differenceSet = new XSet(a);      for (const bValue of b) {        if (a.has(bValue)) {          differenceSet.delete(bValue);        }      }      return differenceSet;    }    // 返回两个集合的对称差集    static symmetricDifference(a, b) {      // 按照定义，对称差集可以表达为      return a.union(b).difference(a.intersection(b));    }    // 返回两个集合（数组对形式）的笛卡儿积    // 必须返回数组集合，因为笛卡儿积可能包含相同值的对    static cartesianProduct(a, b) {      const cartesianProductSet = new XSet();      for (const aValue of a) {        for (const bValue of b) {          cartesianProductSet.add([aValue, bValue]);        }      }      return cartesianProductSet;    }    // 返回一个集合的幂集    static powerSet(a) {      const powerSet = new XSet().add(new XSet());      for (const aValue of a) {          for (const set of new XSet(powerSet)) {            powerSet.add(new XSet(set).add(aValue));          }        }        return powerSet;      }    }