first in first out

class Node:NSObject{
    let data:T
    init(data:T) {
        self.data = data
    }
    
    var next:Node?
}

///        。
class FirstInFirstOut {
    private var head:Node? = nil
    private var rear:Node? = nil
    private(set) var count:Int = 0
    
    var isEmpty:Bool{
        return count == 0
    }
    
    ///     
    func push(object:T){
        if isEmpty {
            head = Node(data: object)
            head?.next = nil
            
            rear = head
            
        }else{
            rear?.next = Node(data: object)
            rear = rear?.next
        }
        count += 1
    }
    
    ///    
    func pop() -> T?{
        guard !isEmpty else {
            return nil
        }
        
        let res = head!.data
        head = head?.next
        
        count -= 1
        
        return res
    }
}