单链表 双链表: 生成,反转,遍历,删除

/**
 * 链表的操作
 */
public class ReverseOfLink {

    public static void main(String[] args) {
        int[] arr = {3, 3, 3, 2, 5, 8, 3, 5, 3, 3, 3, 9};
        //Node head = generateDualLike(arr);
        Node head = generateSingleLink(arr);
        //list(head);
        //Node node = reverseSingleLink(head);
        //Node node = reverseDualLink(head);
        Node node = removeNode(head, 3);
        list(node);
    }

    /*可能会删除头部,链表中也可能有连续的删除节点,所以需要返回新的head*/
    public static Node removeNode(Node head, int val) {
        if(head == null){
            return null;
        }
        //让head来到第一个不需要删除的节点
        /*3, 3, 3, 2, 5, 8, 3, 5, 3, 3, 3, 9*/
        while (head.val == val){
            head = head.next;
        }
        /*节点变成: 2, 5, 8, 3, 5, 3, 3, 3, 9*/
        //TODO: 实现删除逻辑

        
        return head;
    }


    /*反转单项链表*/
    public static Node reverseSingleLink(Node head) {
        Node pre = null;
        Node nxt;
        while (head != null) {
            nxt = head.next;
            head.next = pre;
            pre = head;
            head = nxt;
        }
        return pre;
    }

    /*反转双向链表*/
    public static Node reverseDualLink(Node head) {
        if (head == null) {
            return null;
        }
        Node last = null;
        Node next;
        while (head != null) {
            next = head.next;
            head.next = last;
            head.prev = next;
            last = head;
            head = next;
        }
        return last;
    }

    /*生成单向链表*/
    public static Node generateSingleLink(int[] arr) {
        Node head = new Node(arr[0]);
        for (int i = 1; i < arr.length; i++) {
            addSingleLinkNode(head, arr[i]);
        }
        return head;
    }

    /*生成双向链表*/
    public static Node generateDualLink(int[] arr) {
        Node head = new Node(arr[0]);
        for (int i = 1; i < arr.length; i++) {
            addDualLinkNode(head, arr[i]);
        }
        return head;
    }

    /*添加单链表节点*/
    public static void addSingleLinkNode(Node head, int val) {
        if (head == null) {
            System.out.println("链表头节点为空");
            return;
        }
        if (head.next == null) {
            head.next = new Node(val);
            return;
        }
        Node index = head;
        while (true) {
            if (index.next == null) {
                index.next = new Node(val);
                return;
            } else {
                index = index.next;
            }
        }
    }

    /*添加双向链表节点*/
    public static void addDualLinkNode(Node head, int val) {
        if (head == null) {
            System.out.println("链表头节点为空");
            return;
        }
        if (head.next == null) {
            Node node = new Node(val);
            head.next = node;
            node.prev = head;
            return;
        }
        Node index = head;
        while (true) {
            if (index.next == null) {
                Node node = new Node(val);
                index.next = node;
                node.prev = index;
                return;
            } else {
                index = index.next;
            }
        }
    }

    /*遍历链表*/
    public static void list(Node head) {
        if (head == null) {
            System.out.println("链表为空");
            return;
        }
        Node index = head;
        while (index != null) {
            System.out.println(index.val);
            index = index.next;
        }
    }

    /*节点*/
    private static class Node {
        int val;
        Node next;
        Node prev;

        public Node(int val) {
            this.val = val;
        }
    }
}