复制含有随机指针节点的链表------牛客网初级班练习13

【题目】 一种特殊的链表节点类描述如下：

public class Node {

          public int value;

          public Node next;

          public Node rand;

          public Node(int data) {

                     this.value = data;

          }

}

Node类中的value是节点值，next指针和正常单链表中next指针的意义 一 样，都指向下一个节点，rand指针是Node类中新增的指针，这个指 针可 能指向链表中的任意一个节点，也可能指向null。 给定一个由 Node节点类型组成的无环单链表的头节点head，请实现一个 函数完成 这个链表中所有结构的复制，并返回复制的新链表的头节点。 进阶： 不使用额外的数据结构，只用有限几个变量，且在时间复杂度为 O(N) 内完成原问题要实现的函数。

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);
      map.get(cur).rand = map.get(cur.rand);
      cur = cur.next;
   }
   return map.get(head);
}

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;
      cur.next = next;
      curCopy.next = next != null ? next.next : null;
      cur = next;
   }
   return res;
}

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("=========================");

}