let friendGroupA = ["철수", "영희", "멍멍", "야옹"]
let friendGroupB = ["철수", "영희", "짹짹", "우엉"]
let friendGroupASet = Set(friendGroupA)
let friendGroupBSet = Set(friendGroupB)
let totalFriend = friendGroupASet.union(friendGroupBSet)
//["철수", "영희", "멍멍", "야옹", "짹짹", "우엉"]