第一次测试

1. 将下面的数组进行排序：
   let fruits = [“apple”, “orange”, “pine”, “banana”]

let fruits = ["apple", "orange", "pine", "banana"]
let sortedFruits = fruits.sort(<)
print(sortedFruits)

2. 找出下面数组中年龄大于20的人，并打印姓名：
   let workers = [["name":"Zhangsan", "age":18]，["name":"Lisi", "age":22],
   ["name":"Wangwu", "age":24],
   ["name":"Zhaoliu", "age":16]]

let workers = [
    ["name":"Zhangsan", "age":18],
    ["name":"Lisi", "age":22],
    ["name":"Wangwu", "age":24],
    ["name":"Zhaoliu", "age":16]
]
//struct(值类型): class（类）
//Int/Double: NSNumber
//String: NSString
//Array: NSArray/NSMutableArray
//Dictionary: NSDictionary/NSMutableDictionary
let result = workers.filter({
    (w: [String:NSObject]) -> Bool in
    if w["age"] as! Int > 20 {
        return true
    }
    else {
        return false
    }
})
for w in result {
    print(w["name"]!)
}
//简写
workers.filter({ $0["age"] as! Int > 20 }).forEach({
    print($0["name"]!)
})

3. 请编写代码判断以下数组中的元素是否唯一(没有重复数据)：
   let ids = [1, 9, 3, 7, 2, 3]

let ids = [1, 9, 3, 7, 2, 3]
for n in 0..<ids.count{
    var flag = false
    
    for i in (n+1)..<ids.count
    {
        if ids[n] == ids[i]
        {
            print( "该数组元素不唯一")
            flag = true
            break //结束所在的循环
        }
    }
    if flag {
        break
    }
}

4. 用map/filter/reduce将下面数组中小于60的分数挑出来，并连接成字符串，其中分数之间用逗号隔开：
   let scores = ["30", "61", "59", "89", "99", "20"]

let scores = ["30", "61", "59", "89", "99", "20"]
//map: 转换类型
//filter: 过滤
//reduce: 合成一个
//forEach: 遍历
let r = scores.map({ Int($0)! }).filter({ $0 > 60 }).reduce("", combine: {
    if $0 == "" {
        return "\($1)"
    }
    return "\($0),\($1)"
})
print(r)

5. 定义一个类表示圆，储存它的半径，需要使用时能够快速获取圆的面积，并能够知道半径改变的时机：

class Circle {
    var radius: Double = 0 {
        willSet {
            print("\(radius) -> \(newValue)")
        }
        didSet {
            print("改变完成")
        }
    } 
    var area: Double {
        get {
            return 3.14 * radius * radius
        }
    }
}

6.定义一个协议(protocol),里面包含一个printInfo的方法，然后让Int类型实现该协议(可以随便打印一些东西)：

protocol X {
    func printInfo()
}
//让一个已经存在的类型实现协议，只能通过extension
extension Int : X {
    func printInfo() {
        print("打印一些东西")
    }
}

self：特指调用该方法的"对象"
typealias：给A类型起别名
typealias B = A