1、将数组中每个元素的值乘以 2
let arr = (1...20).map{$0*2}
print(arr)
2、求一组数字的和
print((1...20).reduce(0, +))
3、找到数组中最小（或最大）的元素
let aaa = [10,-22,753,55,137,-1,-279,1034,77]
//Find the minimum of an array of Ints
print(aaa.sorted().first ?? 0)//-279
print(aaa.reduce(Int.max, min))//-279
print(aaa.min() ?? 0) //-279
//Find the maximum of an array of Ints
print(aaa.sorted().last ?? 0)//1034
print(aaa.reduce(Int.min, max))//1034
print(aaa.max() ?? 0)//1034
4、使用析构交换元组中的值
var a1 = 1, b1 = 2
(a1,b1) = (b1,a1)
print(a1, b1)
5、证明字符串中含有某个单词
let words = ["Swift","iOS","cocoa","OSX","tvOS"]
let tweet = "This is an example tweet larking about Swift"
//方法1:
print(!words.filter({tweet.contains($0)}).isEmpty) //true
//方法2:
print(words.contains(where: tweet.contains))// true
//方法3:
let result = tweet.characters
.split(separator: " ")
.lazy
.map(String.init)
.contains(where: Set(words).contains)
print(result)// true
6、埃拉托色尼选筛法（就是求小于N的所有质数）
let n = 50
var primes = Set(2...n)
(2...Int(sqrt(Double(n)))).forEach {
let _ = primes.subtract(stride(from: 2*$0, through: n, by: $0))
}
print(primes.sorted())