逆转一个线性链表

1. 递归法:

        /// <summary>
        /// Reverse linked list by recursion
        /// </summary>
        /// <param name="head"></param>
        public static LinkNode<T> Reverse_Recursion(LinkNode<T> head)
        {
            if (head == null || head.Next == null)
            {
                return head;
            }

            LinkNode<T> node = Reverse_Recursion(head.Next);
            head.Next.Next = head;
            head.Next = null;

            return node;
        }

2. 非递归法:

        /// <summary>
        /// Reverse linked list
        /// </summary>
        /// <param name="head"></param>
        /// <returns></returns>
        public static LinkNode<T> Reverse(LinkNode<T> head)
        {
            if (head == null || head.Next == null)
            {
                return head;
            }

            var currentNode = head.Next;
            var previousNode = head;
            LinkNode<T> nextNode = null;

            previousNode.Next = null;
            while (currentNode != null)
            {
                nextNode = currentNode.Next;
                currentNode.Next = previousNode;

                previousNode = currentNode;
                currentNode = nextNode;
            }

            return previousNode;
        }

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