差集

object B  {
  def main=(args:Array[String]):Unit ={
    val set1 = scala.collection.mutable.selt("apple", "grape", "apple", "pear")
    set1 += "banana"
    set1 -="grape"
    if (set1.contains("apple")){
      println("apple 存在")
    }
    val set2 = scala.collection.mutable.Set("orange")
    val set3 = set1.union(set2)
    println(set3)
    val course = scala.collection.immutable.Set("apple", "banana")
    var newCourse = course + "pear"
    println(newCourse)

  }