[LeetCode] - Copy List with Random Pointer-优快云博客

本文链接：https://blog.youkuaiyun.com/smallfish_yy/article/details/19061857

本文介绍一种深拷贝含随机指针链表的三步法：首先复制节点并插入原节点后；接着复制随机指针；最后分离原链表与拷贝链表。该方法巧妙高效。

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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.

经典问题。分三步，很巧妙。

1. 在原链表的每个node后面插入一个与这个node具有相同值的node，即将原链表复制一遍。这一步相当于对原链表中的node和next指针进行了deep copy。

2. 拷贝random指针。这里是这个算法的精华所在，一言以蔽之，temp.next.random = temp.random.next。

3. 将deep copy的list从原list中挑出来。

代码如下：

/**
 * 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;
        insertNode(head);
        copyRandomPointer(head);
        return getCopyList(head);
    }
    
    public void insertNode(RandomListNode head) {
        RandomListNode temp = head;
        while(temp != null) {
            RandomListNode copyNode = new RandomListNode(temp.label);
            copyNode.next = temp.next;
            temp.next = copyNode;
            temp = temp.next.next;
        }
        return;
    }
    
    public void copyRandomPointer(RandomListNode head) {
        RandomListNode temp = head;
        while(temp != null) {
            if(temp.random==null) temp.next.random=null;
            else temp.next.random=temp.random.next;
            temp = temp.next.next;
        }
        return;
    }
    
    public RandomListNode getCopyList(RandomListNode head) {
        RandomListNode copyList=new RandomListNode(-1), temp=head, copy=copyList;
        while(temp != null) {
            copy.next = temp.next;
            copy = copy.next;
            temp.next = copy.next;
            copy.next = null;
            temp = temp.next;
        }
        return copyList.next;
    }
}