話不多說，先貼作業要求

因為Person類需要一個列舉型別的gender，所以先定義列舉

//性別的列舉
enum Gender: Int {
    case male    //男性
    case female  //女性
    case unknow  //未知
    
    //過載>操作符，方便後面排序使用
    static func >(lhs: Gender, rhs: Gender) -> Bool {
        return lhs.rawValue < rhs.rawValue
    }
}

//人類
class Person: CustomStringConvertible  {
    var firstName: String  //姓
    var lastName: String  //名
    var age: Int  //年齡
    var gender: Gender  //性別
    
    var fullName: String {  //全名
        get {
            return firstName + lastName
        }
    }
    
    //構造方法
    init(firstName: String, lastName: String, age: Int, gender: Gender) {
        self.firstName = firstName
        self.lastName = lastName
        self.age = age
        self.gender = gender
    }
    
    convenience init(firstName: String, age: Int, gender: Gender) {
        self.init(firstName: firstName, lastName: "", age: age, gender: gender)
    }
    
    convenience init(firstName: String) {
        self.init(firstName: firstName, age: 0, gender: Gender.unknow)
    }
    
    required convenience init() {
        self.init(firstName: "")
    }
    
    //過載==
    static func ==(lhs: Person, rhs: Person) -> Bool {
        return lhs.fullName == rhs.fullName && lhs.age == rhs.age && lhs.gender == rhs.gender
    }
    
    //過載!=
    static func !=(lhs: Person, rhs: Person) -> Bool {
        return !(lhs == rhs)
    }
    
    //實現CustomStringConvertible協議中的計算屬性，可以使用print直接輸出物件內容
    var description: String {
        return "fullName: \(self.fullName), age: \(self.age), gender: \(self.gender)"
    }
}

var p1 = Person(firstName: "張")
var p2 = Person(firstName: "張", age: 20, gender: .male)
print(p1)  //輸出fullName: 張, age: 0, gender: male
print(p1 == p2)  //輸出false
print(p1 != p2)  //輸出true
 

//教師類
class Teacher: Person {
    var title: String  //標題
    
    //構造方法
    init(title: String, firstName: String, lastName: String, age: Int, gender: Gender) {
        self.title = title
        super.init(firstName: firstName, lastName: lastName, age: age, gender: gender)
    }
    
    init(title: String) {
        self.title = title
        super.init(firstName: "", lastName: "", age: 0, gender: .unknow)
    }
    
    convenience required init() {
        self.init(title: "")
    }
    
    //重寫父類的計算屬性
    override var description: String {
        return "title: \(self.title), fullName: \(self.fullName), age: \(self.age), gender: \(self.gender)"
    }
}

var t1 = Teacher(title: "hello")
print(t1)  //輸出title: hello, fullName: , age: 0, gender: unknow
 

//學生類
class Student: Person {
    var stuNo: Int  //學號
    
    //構造方法
    init(stuNo: Int, firstName: String, lastName: String, age: Int, gender: Gender) {
        self.stuNo = stuNo
        super.init(firstName: firstName, lastName: lastName, age: age, gender: gender)
    }
    
    init(stuNo: Int) {
        self.stuNo = stuNo
        super.init(firstName: "", lastName: "", age: 0, gender: Gender.unknow)
    }
    
    required convenience init() {
        self.init(stuNo: 0)
    }
    
    //重寫父類的計算屬性
    override var description: String {
        return "stuNo: \(self.stuNo), fullName: \(self.fullName), age: \(self.age), gender: \(self.gender)"
    }
}

var s1 = Student(stuNo: 2015110101)
print(s1)  //輸出stuNo: 2015110101, fullName: , age: 0, gender: unknow
 

//初始化一個空的Person陣列
var array = [Person]()

//生成5個Person物件
for i in 1...5 {
    let temp = Person(firstName: "張", lastName: "\(i)", age: 20, gender: .male)
    array.append(temp)
}
//生成3個Teacher物件
for i in 1...3 {
    let temp = Teacher(title: "hello", firstName: "李", lastName: "\(i)", age: 21, gender: .female)
    array.append(temp)
}
//生成4個Student物件
for i in 1..<5 {
    let temp = Student(stuNo: 2015110100 + i, firstName: "王", lastName: "\(i)", age: 19, gender: .male)
    array.append(temp)
}

//定義一個字典，用於統計每個類的物件個數
var dict = ["Person": 0, "Teacher": 0, "Student": 0]

for item in array {
    if item is Teacher {  //是否是Teacher類
        dict["Teacher"]! += 1
    } else if item is Student {  //是否是Student
        dict["Student"]! += 1
    } else {  //Person類
        dict["Person"]! += 1
    }
}

//輸出字典值
for (key, value) in dict {
    print("\(key) has \(value) items")
}

//原始陣列
print("------------------------------")
for item in array {
    print(item)
}

//根據age從大到小排序
print("------------------------------")
array.sort { return $0.age > $1.age}
for item in array {
    print(item)
}

//根據全名從前往後排序
print("------------------------------")
array.sort { return $0.fullName < $1.fullName}
for item in array {
    print(item)
}

//根據gender和age從大往小排序
print("------------------------------")
array.sort { return ($0.gender > $1.gender) && ($0.age > $1.age) }
for item in array {
    print(item)
}