LeetCode – 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.

/**
 * 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;
        RandomListNode p=head;
//拷贝当前节点，并将其插入到被拷贝节点的后方
        while(p!=null){
            RandomListNode temp=new RandomListNode(p.label);
            temp.next=p.next;
            p.next=temp;
            p=temp.next;
        }
        p=head;
//将拷贝节点的随机指针指向应有位置
        while(p!=null){
            if(p.random!=null){
                p.next.random=p.random.next;
            }
            p=p.next.next;
        }
        RandomListNode newhead=head.next;
        p=head;
//将拷贝链表与原链表分离
        while(p!=null){
            RandomListNode temp=p.next;
            p.next=temp.next;
            if(temp.next!=null)
                temp.next=temp.next.next;
            p=p.next;
        }
        return newhead;
    }
}

最后分离也可这样写：

while(p != null && p.next != null){
    RandomListNode temp = p.next;
    p.next = temp.next;
    p = temp;
}

解法2：

可以用hashmap的方式

public RandomListNode copyRandomList(RandomListNode head) {
    if (head == null)
        return null;
    HashMap<RandomListNode, RandomListNode> map = new HashMap<RandomListNode, RandomListNode>();
    RandomListNode newHead = new RandomListNode(head.label);
 
    RandomListNode p = head;
    RandomListNode q = newHead;
    map.put(head, newHead);
 
    p = p.next;
    while (p != null) {
        RandomListNode temp = new RandomListNode(p.label);
        map.put(p, temp);
        q.next = temp;
        q = temp;
        p = p.next;
    }
 
    p = head;
    q = newHead;
    while (p != null) {
        if (p.random != null)
            q.random = map.get(p.random);
        else
            q.random = null;
 
        p = p.next;
        q = q.next;
    }
 
    return newHead;
}