[Java]LeetCode138. 复制带随机指针的链表 | Copy List with Random Pointer

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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.

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给定一个链表，每个节点包含一个额外增加的随机指针，该指针可以指向链表中的任何节点或空节点。

要求返回这个链表的深度拷贝。 

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1ms

/**
 * 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) {
        RandomListNode res = new RandomListNode(0);
        RandomListNode p = res;
        RandomListNode curr = head;
        while (curr != null) {
            p.next = clone(curr);
            curr = curr.next;
            p = p.next;
        }
        return res.next;
    }
    
    private RandomListNode clone(RandomListNode node) {
        RandomListNode newNode = new RandomListNode(node.label);
        if (node.random != null)
            newNode.random = new RandomListNode(node.random.label);
        return newNode;
    }
}

---

2ms

/**
 * 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;
        copyNext(head);
        copyRandom(head);
        
        RandomListNode curr = head;
        RandomListNode newHead = head.next;
        RandomListNode start = newHead;
        while(curr!=null && curr.next!=null){
            RandomListNode next = curr.next.next;
            curr.next = next;
            curr = next;
            
            if(start.next!=null) {
                start.next = start.next.next;
                start = start.next;
            }
        }
        
        return newHead;
    }
    
    private void copyNext(RandomListNode head){
        if(head == null) return;
        
        RandomListNode curr = head;
        while(curr!=null){
            RandomListNode next = curr.next;
            curr.next = new RandomListNode(curr.label);
            curr.next.random = curr.random;
            curr.next.next = next;
            curr = next;
        }
    }
    
    private void copyRandom(RandomListNode head) {
        if(head == null) return;
        RandomListNode curr = head;
        while(curr!=null && curr.next!=null){
            RandomListNode next = curr.next.next;
            if(curr.next!=null && curr.random!=null){
                curr.next.random = curr.random.next;
            }
            curr = next;
        }
    }
}

---

2ms

/**
 * 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) 
    {
        RandomListNode root = null, prev = null, rootIter = head;
        
        while (rootIter != null)
        {
            RandomListNode newCopy = new RandomListNode(rootIter.label);
            newCopy.next = null;
            newCopy.random = null;
            
            prev = rootIter;
            rootIter = rootIter.next;
            
            prev.next = newCopy;
            newCopy.next = rootIter;
            /* 'prev' points to previous rootIter whose 'next' will point
            to the new copy of previous rootIter created in 'newCopy' */
        }
        if (head == null)
            root = null;
        
        else
            root = head.next;
        
        rootIter = head;
        while (rootIter != null)
        {
            if (rootIter.random == null)
                rootIter.next.random = null;
            
            else
                rootIter.next.random = rootIter.random.next;
            
            rootIter = rootIter.next.next;
        }
        
        rootIter = head;
        while (rootIter != null)
        {
            RandomListNode nextNode = rootIter.next.next;
            if (nextNode != null)
                rootIter.next.next = nextNode.next;
            
            rootIter.next = nextNode;
            rootIter = nextNode;  
        }
        return root;
    }
}

---

3ms

/**
 * 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 {
    
    private Map<RandomListNode,RandomListNode> visited = new HashMap<>(); 
    
    public RandomListNode copyRandomList(RandomListNode head) {
        if(head == null){
            return null;
        }
        
        if(visited.containsKey(head)){
            return visited.get(head); 
        }
        
        RandomListNode newNode = new RandomListNode(head.label); 
        visited.put(head,newNode); //at this point in time, we have newed this node. does not matter if we need to recurse further to have it fully constructed. this is already copied. thus mark it as visited
        
        newNode.next = copyRandomList(head.next); 
        newNode.random = copyRandomList(head.random); 
        
        
        return newNode; 
        
    }
}