swift 数组 的一些快速方法

1. filter (过滤器)：返回符合条件的一个数组
                let arr = [1,5,6,7,10,0]
               //写法1
                let arr1 = arr.filter { (item) -> Bool in
                    return item % 2 == 0
                }
               
                 //写法2
                let resultArray = arr.filter { return $0%2 == 0 }
    
                 //写法3
                let arr2 = arr.filter({return $0%2 == 0})

2.index(符合条件的索引)：返回int值
                let arr = [1,0]
                //写法1：swift 4.0
                let index = arr.index(where: {$0 == 1})
                
                //swift4.2  firstIndex:从前往后遍历，
                let index2 = arr.firstIndex(where:{$0 == 1})
                let index3 = arr.firstIndex { (item) -> Bool in
                    return item == 1
                }
                
                //lastIndex:c从后往前遍历
                let index4 = arr.lastIndex(where:{$0 == 1})
                
                let index5 = arr.lastIndex(of: 5)
                if index5 != nil{
                    print("打印一下")
                }

3. contains(包含)：返回bool值
                let arr = [1,0]
                //写法1
                let isContains = arr.contains(where: {$0 == 3})
                //写法2
                let isContains1 = arr.contains { (item) -> Bool in
                    return item == 100
                }
                //写法3 直接调用函数
                 arr.contains(10)
                print(arr.contains(3))