Solution35.java

/*
// Definition for a Node.
class Node {
    int val;
    Node next;
    Node random;

    public Node(int val) {
        this.val = val;
        this.next = null;
        this.random = null;
    }
}
*/
class Solution {
    public Node copyRandomList(Node head) {
        if (head == null) {
            return null;
        }
        copy(head);
        randomDirect(head);
        return reList(head);
    }

    // 拷贝链表
    private void copy(Node head) {
        while (head != null) {
            Node cloneNode = new Node(head.val);
            Node nextNode = head.next;
            head.next = cloneNode;
            cloneNode.next = nextNode;
            head = cloneNode.next;
        }
    }

    // 指定随机指针
    private void randomDirect(Node head) {
        while (head != null) {
            Node cloneNode = head.next;
            if (head.random != null) {
                Node direct = head.random;
                cloneNode.random = direct.next;
            }
            head = cloneNode.next;
        }
    }

    // 重新连接 链表
    private Node reList(Node head) {
        Node cloneNode = head.next;
        Node cloneHead = cloneNode;
        head.next = cloneNode.next;
        head = head.next;
        while (head != null) {
            cloneNode.next = head.next;
            head.next = head.next.next;
            head = head.next;
            cloneNode = cloneNode.next;
        }

        return cloneHead;
    }
}