138. Copy List With Random Pointer

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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.

解法1： HashMap

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/**
 * 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;
        }
        Map<RandomListNode, RandomListNode> map = new HashMap<>();
        RandomListNode oldHead = head;
        while (head != null) {
            RandomListNode copy = new RandomListNode(head.label);
            map.put(head, copy);
            head = head.next;
        }
        head = oldHead;
        while (head != null) {
            map.get(head).random = map.get(head.random);
            if (head.next != null) {
                map.get(head).next = map.get(head.next);
            }
            head = head.next;
        }
        return map.get(oldHead);
    }
}