复制带random结点的链表

题目：

image.png

思路1：

建立一个辅助的HashMap<Node,Node> 存储当前结点和他的复制结点，然后把他们的复制结点连接，然后再复制rand，在这里注意复制random，复制节点的random指向的也是复制结点，所以注意赋值的操作，具体看代码

代码1：

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

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

    public static Node copyListWithRand1(Node head) {
        HashMap<Node, Node> map = new HashMap<Node, Node>();
        Node cur = head;
        while (cur != null) {
            map.put(cur, new Node(cur.value));
            cur = cur.next;
        }
        cur = head;
        while (cur != null) {
            map.get(cur).next = map.get(cur.next);
                        //注意！，复制结点的random也是复制结点
            map.get(cur).rand = map.get(cur.rand);
            cur = cur.next;
        }
        return map.get(head);
    }

思路2：

将每个复制结点放到当前结点的后面，整理过后是如下的格式：

1->1'->2->2'->3->3'

整理过后赋值random结点，在这里也要注意，连同上面的建立过程，不要忘了让1'指向2这个过程
然后分离新建复制链表，注意每个节点的指向，都要思考到，不能出现空指向。

代码2：

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

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

public static Node copyListWithRand2(Node head) {
        if (head == null) {
            return null;
        }
        Node cur = head;
        Node next = null;
        // copy node and link to every node
        while (cur != null) {
            next = cur.next;
            cur.next = new Node(cur.value);
            cur.next.next = next;
            cur = next;
        }
        cur = head;
        Node curCopy = null;
        // set copy node rand
        while (cur != null) {
            next = cur.next.next;
            curCopy = cur.next;
            curCopy.rand = cur.rand != null ? cur.rand.next : null;
            cur = next;
        }
        Node res = head.next;
        cur = head;
        // split
        while (cur != null) {
            next = cur.next.next;
            curCopy = cur.next;
            //注意这里，复原光复原复制链表还有原链表
            cur.next = next;
            curCopy.next = next != null ? next.next : null;
            cur = next;
        }
        return res;
    }

测试用例：

    public static void printRandLinkedList(Node head) {
        Node cur = head;
        System.out.print("order: ");
        while (cur != null) {
            System.out.print(cur.value + " ");
            cur = cur.next;
        }
        System.out.println();
        cur = head;
        System.out.print("rand:  ");
        while (cur != null) {
            System.out.print(cur.rand == null ? "- " : cur.rand.value + " ");
            cur = cur.next;
        }
        System.out.println();
    }

    public static void main(String[] args) {
        Node head = null;
        Node res1 = null;
        Node res2 = null;
        printRandLinkedList(head);
        res1 = copyListWithRand1(head);
        printRandLinkedList(res1);
        res2 = copyListWithRand2(head);
        printRandLinkedList(res2);
        printRandLinkedList(head);
        System.out.println("=========================");

        head = new Node(1);
        head.next = new Node(2);
        head.next.next = new Node(3);
        head.next.next.next = new Node(4);
        head.next.next.next.next = new Node(5);
        head.next.next.next.next.next = new Node(6);

        head.rand = head.next.next.next.next.next; // 1 -> 6
        head.next.rand = head.next.next.next.next.next; // 2 -> 6
        head.next.next.rand = head.next.next.next.next; // 3 -> 5
        head.next.next.next.rand = head.next.next; // 4 -> 3
        head.next.next.next.next.rand = null; // 5 -> null
        head.next.next.next.next.next.rand = head.next.next.next; // 6 -> 4

        printRandLinkedList(head);
        res1 = copyListWithRand1(head);
        printRandLinkedList(res1);
        res2 = copyListWithRand2(head);
        printRandLinkedList(res2);
        printRandLinkedList(head);
        System.out.println("=========================");

    }