138. Copy List with Random Pointer

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.

思路：复制一个map先

/**
 * 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 null;
        Map<RandomListNode, RandomListNode> map = new HashMap<RandomListNode,RandomListNode>();

        // loop 1. copy all the nodes
        RandomListNode node = head;
        while (node!=null){
            map.put(node, new RandomListNode(node.label));
            node = node.next;
        }

        // loop 2. assign next and random pointers
        node = head;
        while (node!=null){
            map.get(node).next = map.get(node.next);
            map.get(node).random = map.get(node.random);
            node = node.next;
        }

        return map.get(head);
    }
}