基础数据结构--链表的练习

一、单链表和双链表反转

public class ReverseNode {

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

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

    public static class DoubleNode {
        public int value;
        public DoubleNode last;
        public DoubleNode next;

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

    /**
     * 单链表反转
     * a   ->   b   ->  c  ->  null
     * c   ->   b   ->  a  ->  null
     *
     * @return 返回头节点
     */
    public static Node reverseNode(Node head) {
        Node pre = null;
        Node next = null;
        while (head != null) {
            next = head.next;
            head.next = pre;
            pre = head;
            head = next;
        }
        return pre;
    }

    public static DoubleNode reverseDoubleNode(DoubleNode head) {
        DoubleNode pre = null;
        DoubleNode next = null;

        while (head != null) {
            next = head.next;
            head.next = pre;
            head.last = next;
            pre = head;
            head = next;
        }

        return pre;
    }

}

核心点：

（1）单链表：

拿到next节点，修改当前节点的next节点，拿到pre节点，当前节点后移

（2）双链表：

拿到next节点，修改当前节点的next、last节点，拿到pre节点，当前节点后移

二、单链表删除指定的值

public class DeleteNodeValue {

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

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

    public static Node removeValue(Node head, int num) {
        while (head != null) {
            if (head.value != num) {
                break;
            }
            head = head.next;
        }

        Node pre = head;
        Node cur = head;
        while (cur != null) {
            if (cur.value == num) {
                pre.next = cur.next;
            } else {
                pre = cur;
            }
            cur = cur.next;
        }

        return head;
    }

}

核心点：

1）找到不需要删除值的节点作为头节点（最后返回此头节点）

2）标记pre和cur节点

3）从cur开始挨个遍历剩下的节点

如果cur节点的值等于要删除的值，则修改pre节点的next节点；

如果cur节点的值不是要删除的值，则将pre节点修改为cur节点。