判断一个字符串是否为回文-链队(新建，进队，出队)，链栈(新建，进栈，出栈)

回文：字符对称排列的字符串，例如ABCBA

思路：根据队：先进先出和栈: 先进后出的原则，进行比较出队和出栈的字符是否相等。如果相等，则为回文。

创建控制台应用程序。

        #region 字符节点类 
        class CharNode
        {
            public char Char    //字符
            {
                get;
                set;
            }
            public CharNode Next   //下一节点
            {
                get;
                set;
            }
            public CharNode(char Char,CharNode next)
            {
                this.Char = Char;
                this.Next = next;
            }
        }

        #endregion

        #region 链队类 
        /// <summary>
        /// 链队
        /// </summary>
        class CharQueue
        {
            CharNode front;  //队头
            CharNode rear;   //队尾
            /// <summary>
            /// 进队 
            /// </summary>
            /// <param name="Char">节点字符</param>
            public void In(char Char)
            {
                if(rear==null)
                {
                    rear= new CharNode(Char, null);      //创建队头节点
                    front = rear;
                }
                else
                {
                    rear.Next = new CharNode(Char, null);     //创建队尾
                    rear = rear.Next;
                }
            }

            /// <summary>
            /// 出队
            /// </summary>
            /// <returns></returns>
            public char? Out()
            {
                if(front==null)
                {
                    return null;
                }

                char Char = front.Char;
                front = front.Next;
                if (front == null)
                    rear = null;

                return Char;

            }

        }
        #endregion

        #region 链栈类
        public class CharStack
        {
            CharNode top;
            /// <summary>
            /// 进栈
            /// </summary>
            /// <param name="Char">节点字符</param>
            public void Push(char Char)
            {
              
                if(top==null)
                {
                    top = new CharNode(Char, null);
                }
                else
                {
                    top = new CharNode(Char, top);
                }
            }
            /// <summary>
            /// 出栈
            /// </summary>
            /// <returns></returns>
            public char? Pop()   //？代表可以返回null
            {
                if (this.top == null)
                    return null;
                else
                {
                    char Char = top.Char;
                    top = top.Next;
                    return Char;
                }
            }
        }         

        #endregion
        static void Main(string[] args)
        {
            Console.WriteLine("pls input one string:");
            string str = Console.ReadLine();
            CharStack stack = new CharStack();   //实例化栈
            CharQueue queue = new CharQueue();   //实例化队 

            char? charStack, charQueue;

            foreach(char Char in str)   
            {
                queue.In(Char);     //进队
                stack.Push(Char);   //进栈
            }

            do
            {
                charQueue = queue.Out();  //出队
                charStack = stack.Pop();   //出栈

                if (charQueue != charStack)
                    break;
            }
            while (charQueue != null && charStack != null);

            if(charQueue!=null||charStack!=null)
            {
                Console.WriteLine("{0} is not 回文",str);
            }
            else
            {
                Console.WriteLine("{0} is 回文 ",str);
            }

            Console.ReadLine();
            
        }