138. Copy List with Random Pointer

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本文介绍了一种含有额外随机指针的单链表的深拷贝方法。提出了两种解决方案：一种通过穿插复制节点并重新链接，另一种使用哈希映射来保存节点及其副本之间的对应关系。

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A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.

Return a deep copy of the list.

/**
 * Definition for singly-linked list with a random pointer.
 * class RandomListNode {
 *     int label;
 *     RandomListNode next, random;
 *     RandomListNode(int x) { this.label = x; }
 * };
 */
public class Solution {
    public RandomListNode copyRandomList(RandomListNode head) {
        if (head  == null) return head;
        RandomListNode node = head;
        while (node != null) {
            RandomListNode tmp = node.next;
            RandomListNode add = new RandomListNode(node.label);
            add.next = node.next;
            node.next = add;
            node = tmp;
        }
        node = head;
        while (node != null) {
            if (node.random != null) node.next.random = node.random.next;
            node = node.next.next;
        }
        RandomListNode dummy = new RandomListNode(0);
        RandomListNode cursor = dummy;
        node = head;
        while (node != null) {
            RandomListNode tmp = node.next.next;
            cursor.next = node.next;
            cursor = cursor.next;
            node.next = tmp;
            node = tmp;
        }
        return dummy.next;
    }
}

/**
 * Definition for singly-linked list with a random pointer.
 * class RandomListNode {
 *     int label;
 *     RandomListNode next, random;
 *     RandomListNode(int x) { this.label = x; }
 * };
 */
public class Solution {
    public RandomListNode copyRandomList(RandomListNode head) {
        if (head  == null) return head;
        HashMap<RandomListNode, RandomListNode> map = new HashMap<>();
        RandomListNode node = head;
        while (node != null) {
            map.put(node, new RandomListNode(node.label));
            node = node.next;
        }
        node = head;
        while (node != null) {
            RandomListNode tmp = map.get(node);
            tmp.next = map.get(node.next);
            tmp.random = map.get(node.random);
            node = node.next;
        }

        return map.get(head);
    }
}