Sequence1

import Foundation



print("Hello, World!")



//protocol IteratorProtocol {

// associatedtype Element

// mutating func next() -> Element?

//}



struct Ones: IteratorProtocol {
    
    typealias Element = Int
    
    mutating func next() -> Int? {
        
        return 1
        
    }
    
}



var ones = Ones()

print(ones.next())

print(ones.next())



//struct Fibonacci: IteratorProtocol {

// typealias Element = Int

//

// private var state = (0, 1)

//

// mutating func next() -> Int? {

// let nextNumber = state.0

// state = (state.1, state.0 + state.1)

// return nextNumber

// }

//

//}

//var fibonacci = Fibonacci()
//print(fibonacci.next())
//print(fibonacci.next())
//print(fibonacci.next())
//print(fibonacci.next())
//print(fibonacci.next())
//print(fibonacci.next())
//
//var fibonacci1 = fibonacci
//print(fibonacci1.next())
//protocol Sequence {
// associatedtype Element

// associatedtype Iterator: IteratorProtocol where Iterator.Element == Element

//

// func makeIterator() -> Iterator

//}



struct FiboIter: IteratorProtocol {
    
    typealias Element = Int
    
    var state = (0, 1)
    
    mutating func next() -> Int? {
        
        let nextNumber = state.0
        
        self.state = (state.1, state.0 + state.1)
        
        return nextNumber
        
    }
    
}



struct Fibonacci: Sequence {
    
    typealias Element = Int
    
    func makeIterator() -> FiboIter {
        
        return FiboIter()
        
    }
    
}



var fibs = Fibonacci()

var fib1 = fibs.makeIterator()

print(fib1.next())

print(fib1.next())

print(fib1.next())

print(fib1.next())

print(fib1.next())

print(fib1.next())

print(fib1.next())



for n in  Fibonacci() {
    
    if n <= 5 {
        
        print(n)
        
    } else {
        
        break
        
    }
    
}



var arrayInt: [Int] = []

var sumInt = arrayInt.reduce(0, +)

print(sumInt)



var arrStr: [String] = []

var sumStr = arrStr.reduce("", +)

print(sumStr)

func reduce1(of sequence: S, _ partical: (E, E) -> E) -> E?
    
    where S: Sequence, E == S.Element {
        
        var iter: S.Iterator = sequence.makeIterator()
        
        guard var accumulated = iter.next() else {
            
            return nil
            
        }
        while let element = iter.next() {
            
            accumulated = partical(accumulated, element)
            
        }
        return accumulated
        
}

extension  Sequence {
    
    //FixedWidthInteger, SignedInteger , 先就这么着吧,:slightly_smiling:
    
    func reduceFromZero(of sequence: S, _ partical: (E, E) -> E) -> E where S: Sequence, E: FixedWidthInteger, E: SignedInteger, E == S.Element {
        
        var iter = sequence.makeIterator()
        
        guard var accumulated = iter.next() else { return 0 }
        
        while let element = iter.next() {
            
            accumulated = partical(accumulated, element)
            
        }
        
        return accumulated
        
    }
    
}



print(reduce1(of: arrayInt, +))



print([1].elementsEqual([1]))
​