Java反轉鏈表（單向鏈表和雙向鏈表）

這是一個常見的考驗 Coding 能力的筆試題。
主要思路就是：
對於每個節點，使用臨時變量記錄原來的前驅和原來的後繼，然後把原來的前驅接到這個節點的後繼上。
代碼如下：

public class ReverseList {

    public static class Node {
        public int value;
        public Node next;

        public Node(int data) {
            this.value = data;
        }
    }

    //單向鏈表反轉
    public static Node reverseList(Node head) {
        //記錄原前驅
        Node pre = null;
        //記錄原後繼的輔助變量
        Node next;
        while (head != null){
            //記錄原後繼
            next = head.next;
            //反轉
            head.next = pre;
            //刷新前驅
            pre = head;
            //刷新當前節點
            head = next;
        }
        //運行到最後pre是新的頭
        return pre;
    }

    public static class DoubleNode {
        public int value;
        //前驅
        public DoubleNode pre;
        //後繼
        public DoubleNode next;

        public DoubleNode(int data) {
            this.value = data;
        }
    }

    //雙向鏈表反轉
    public static DoubleNode reverseList(DoubleNode head) {
        //記錄原前驅
        DoubleNode pre = null;
        //記錄原後繼的變量
        DoubleNode next;
        while (head != null){
            //記錄原後繼
            next = head.next;
            //反轉
            head.next = pre;
            head.pre = next;
            //刷新前驅
            pre = head;
            //刷新當前節點
            head = next;
        }
        //運行到最後pre是新的頭
        return pre;
    }

    public static void printLinkedList(Node head) {
        System.out.print("Linked List: ");
        while (head != null) {
            System.out.print(head.value + " ");
            head = head.next;
        }
        System.out.println();
    }

    public static void printDoubleLinkedList(DoubleNode head) {
        System.out.print("Double Linked List: ");
        DoubleNode end = null;
        while (head != null) {
            System.out.print(head.value + " ");
            end = head;
            head = head.next;
        }
        System.out.print("| ");
        while (end != null) {
            System.out.print(end.value + " ");
            end = end.pre;
        }
        System.out.println();
    }

    public static void main(String[] args) {
        Node head1 = new Node(1);
        head1.next = new Node(2);
        head1.next.next = new Node(3);
        printLinkedList(head1);
        head1 = reverseList(head1);
        printLinkedList(head1);

        DoubleNode head2 = new DoubleNode(1);
        head2.next = new DoubleNode(2);
        head2.next.pre = head2;
        head2.next.next = new DoubleNode(3);
        head2.next.next.pre = head2.next;
        head2.next.next.next = new DoubleNode(4);
        head2.next.next.next.pre = head2.next.next;
        printDoubleLinkedList(head2);
        printDoubleLinkedList(reverseList(head2));

    }

}

運行結果：