[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.

https://oj.leetcode.com/problems/copy-list-with-random-pointer/

 

思路：在每个原来的节点后面插入新节点；复制random指针；分解至两个独立列表

 

public class Solution {
    public RandomListNode copyRandomList(RandomListNode head) {
        if (head == null)
            return null;

        // copy the next
        RandomListNode cur = head;
        while (cur != null) {
            RandomListNode tmp = new RandomListNode(cur.label);
            tmp.next = cur.next;
            cur.next = tmp;
            cur = tmp.next;
        }

        // copy the random pointer
        cur = head;
        while (cur != null) {
            RandomListNode tmp = cur.next;
            if (cur.random != null)
                tmp.random = cur.random.next;
            cur = tmp.next;
        }

        // decomposite
        RandomListNode res = head.next;
        cur=head;
        while (cur != null) {
            RandomListNode tmp = cur.next;
            cur.next = tmp.next;
            if (tmp.next != null)
                tmp.next = tmp.next.next;
            cur = cur.next;
        }

        return res;

    }
    
    
    
}

 

第二遍记录： 

 

第三遍记录：

　　注意复制random的时候，先判断random是否为空

　　注意各个指针的变换，可以建立一些临时节点指针方便操作，比如post。

public class Solution {
    public RandomListNode copyRandomList(RandomListNode head) {
        if(head==null)
            return null;
        RandomListNode cur = head;
        while(cur!=null){
            RandomListNode newNode = new RandomListNode(cur.label);
            newNode.next=cur.next;
            cur.next=newNode; 
            cur=newNode.next;   
        }
        
        cur = head;
        while(cur!=null){
            if(cur.random!=null)
                cur.next.random = cur.random.next;
            cur=cur.next.next;
        }
        
        cur = head;
        RandomListNode res = head.next;
        
        while(cur!=null){
            RandomListNode post =cur.next;
            cur.next=post.next;
            if(cur.next!=null)
                post.next = post.next.next;
            cur =cur.next;
        }
        
        return res;
    
    }
    
}

 

 

 

参考：

http://fisherlei.blogspot.com/2013/11/leetcode-copy-list-with-random-pointer.html