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

遍历list将所有节点new一个出来放到hashmap中，第二遍遍历list将旧的节点对应新节点取出来组成链表就okay了

/**
 * Definition for singly-linked list with a random pointer.
 * class RandomListNode {
 *     int label;
 *     RandomListNode next, random;
 *     RandomListNode(int x) { this.label = x; }
 * };
 */
import java.util.HashMap;
import java.util.Map;

public class Solution {
    public RandomListNode copyRandomList(RandomListNode head) {
        if(head == null)
            return head;
        Map<RandomListNode, RandomListNode> old2new = new HashMap<RandomListNode, RandomListNode>();
        
        //新的头结点
        RandomListNode newHead = new RandomListNode(head.label);
        old2new.put(head, newHead);
        
        RandomListNode tempHead = head.next;                                    //所有的节点放到hashmap中
        while(tempHead != null){
            RandomListNode tempNode = new RandomListNode(tempHead.label);
            old2new.put(tempHead, tempNode);
            tempHead = tempHead.next;
        }//while
        
        RandomListNode tempNewHead = null;
        tempHead = head;
        
        while(tempHead != null){
            tempNewHead = old2new.get(tempHead);
            tempNewHead.next = old2new.get(tempHead.next);
            tempNewHead.random = old2new.get(tempHead.random);
            tempHead = tempHead.next;
            tempNewHead = tempNewHead.next;
        }//while
        
        return newHead;
    }
}