Copy List with Random Pointer

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.

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基本思路：  详细分析过程见 这里 ，提供了三种思路。

按照思路 1 实现，时间复杂度0(n^2)，超时。

思路 2  实现代码如下：

RandomListNode *copyRandomList(RandomListNode *head) {
        
        if(NULL==head){
            return head;
        }
        
        //复制原始链表上的每个链表  并用 next 链接起来
        RandomListNode* Nhead = new RandomListNode(head->label);
        RandomListNode* iter = head;
        RandomListNode* Niter = Nhead;
        map<RandomListNode*,RandomListNode*> NodeMap;
        NodeMap[head] = Nhead;
        
        while(iter->next != NULL){
            Niter->next = new RandomListNode(iter->next->label);
            iter = iter->next;
            Niter = Niter->next;
            
            NodeMap[iter] = Niter;
        }
        
        //定位每个结点的m_pSibling
        iter = head;
        Niter = Nhead;
        while(iter != NULL){
            RandomListNode* TempRand = iter->random;
            if(TempRand==NULL){
                Niter->random = NULL;
            }
            else{
                
                Niter->random = NodeMap[iter->random];
                
            }
            
            iter = iter->next;
            Niter = Niter->next;
        }
        
        return Nhead;
    }

思路三实现参照了这里的代码 。实现过程中有 2 个地方(标注在代码中)需要注意，代码如下：

 void cloneNodes(RandomListNode* head){
        if(NULL==head){
            return;
        }
        
        RandomListNode* iter = head;
        while(iter != NULL){
            RandomListNode* node = new RandomListNode(iter->label);
            
            node->next = iter->next; 
            iter->next = node;
            iter = node->next;
        }
    }
    
    void connectRandomNodes(RandomListNode* head){
        if(NULL==head){
            return;
        }
        
        RandomListNode* iter = head;
        RandomListNode* copyIter = head->next;
        
        while(iter != NULL){
            if(iter->random != NULL){
                copyIter->random = iter->random->next;
            }else{
                copyIter->random = NULL;
            }
            
            iter = copyIter->next;
            
            if(iter != NULL){   // important!!!
                copyIter = iter->next;
            }
        }
    }

    RandomListNode* reconnectNodes(RandomListNode* head){
        if(NULL==head){
            return head;
        }
        
        RandomListNode* iter = head;
        RandomListNode* copyIter = head->next;
        RandomListNode* Nhead = head->next;
        
        while(iter != NULL){
            iter->next = copyIter->next;
            iter = iter->next;
            
            if(iter != NULL){  // important!!!
                copyIter->next = iter->next;
                copyIter = iter->next;
            }
        }
        
        return Nhead;
    }
    
    
    RandomListNode *copyRandomList(RandomListNode *head) {
        cloneNodes(head);
        connectRandomNodes(head);
        return reconnectNodes(head);
    }