public static class Node {
    public int value;
    public Node next;
    public Node(int value) {
        this.value = value;
    }
    @Override
    public String toString() {
        ArrayList<Integer> nums = new ArrayList<>();
        Node node = this;
        while (node != null) {
            nums.add(node.value);
            node = node.next;
        }
        return nums.toString();
    }
}

反轉(zhuǎn)單向鏈表

public static Node reverseLinkedList(Node head) {
    Node next = null;
    Node pre = null;
    while (head != null) {
        next = head.next;
        head.next = pre;
        pre = head;
        head = next;
    }
    return pre;
}

測試函數(shù)

public static void main(String[] args) {
    Node node = new Node(1);
    node.next = new Node(2);
    node.next.next = new Node(3);
    node = reverseLinkedList(node);
    System.out.println(node);
}

輸出結果如下：

[3, 2, 1]

雙向鏈表

Node結點

public static class DoubleList {
    public int value;
    public DoubleList next;
    public DoubleList last;
    public DoubleList(int value) {
        this.value = value;
    }
    @Override
    public String toString() {
        ArrayList<Integer> nums = new ArrayList<>();
        DoubleList node = this;
        while (node != null) {
            nums.add(node.value);
            node = node.next;
        }
        return nums.toString();
    }
}

反轉(zhuǎn)雙向鏈表

public static DoubleList reverseDoubleList(DoubleList head) {
    DoubleList next;
    DoubleList pre = null;
    while (head != null) {
        next = head.next;
        head.next = pre;
        // 注意和單項鏈表不一樣的地方只有這一行，其他都基本一樣
        head.last = next;
        pre = head;
        head = next;
    }
    return pre;
}

測試代碼

public static void main(String[] args) {
    DoubleList node1 = new DoubleList(1);
    node1.next = new DoubleList(2);
    node1.next.last = node1;
    node1.next.next = new DoubleList(3);
    node1.next.next.last = node1.next;
    System.out.println("reverseDoubleList(node1) = " + reverseDoubleList(node1));
}

輸出結果如下：