leetcode No138. Copy List with Random Pointer

Question:

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.

Algorithm:

算法1：

复制原始链表上的每个结点N创建N',然后把这些创建出来的结点用next连接起来。同时我们把<N,N'>的配对信息放到一个哈希表中。第二步，设置每个结点的random指针，如果在原始链表中结点N的random指向结点S,那么在复制链表中，对应的N'应该指向S'。由于有了哈希表，我们可以用O(1)的时间根据S找到S'。

算法2：

第一步，复制原始链表上的每个结点N创建N'，我们把N'链接在N的后面。

第二步，设置复制出来的结点的random指针。

第三步：把长链表拆分成两个链表

Accepted Code：

算法1：

/** * Definition for singly-linked list with a random pointer. * struct RandomListNode { *     int label; *     RandomListNode *next, *random; *     RandomListNode(int x) : label(x), next(NULL), random(NULL) {} * }; */class Solution {public:    RandomListNode *copyRandomList(RandomListNode *head) {        if(head==NULL)            return NULL;        map<RandomListNode*,RandomListNode*> hash;        RandomListNode *pNode=head;        RandomListNode *pCloneHead=new RandomListNode(pNode->label);        RandomListNode *pCloneNode=pCloneHead;        hash[pNode]=pCloneNode;        pNode=pNode->next;        while(pNode)        {            pCloneNode->next=new RandomListNode(pNode->label);            pCloneNode=pCloneNode->next;            hash[pNode]=pCloneNode;            pNode=pNode->next;        }        pCloneNode=pCloneHead;        pNode=head;        while(pCloneNode)        {            pCloneNode->random=hash[pNode->random];            pNode=pNode->next;            pCloneNode=pCloneNode->next;        }        return pCloneHead;    }};

算法2：

/** * Definition for singly-linked list with a random pointer. * struct RandomListNode { *     int label; *     RandomListNode *next, *random; *     RandomListNode(int x) : label(x), next(NULL), random(NULL) {} * }; */class Solution {public:    RandomListNode *copyRandomList(RandomListNode *head) {        if(head==NULL)return NULL;        CloneNodes(head);        ConnectSiblingNodes(head);        return ReconnectNodes(head);    }    void CloneNodes(RandomListNode* pHead)    {        RandomListNode* pNode=pHead;        while(pNode!=NULL){            RandomListNode* temp=pNode->next;            pNode->next=new RandomListNode(pNode->label);            pNode->next->next=temp;            pNode=temp;        }    }    void ConnectSiblingNodes(RandomListNode* pHead)    {    RandomListNode* pNode = pHead;    while (pNode!=NULL){    if (pNode->random == NULL)    pNode->next->random = NULL;    else    pNode->next->random = pNode->random->next;    pNode = pNode->next->next;    }    }    RandomListNode* ReconnectNodes(RandomListNode* pHead)    {    RandomListNode* pNode = pHead;    RandomListNode* pCloneHead = NULL;    RandomListNode* pCloneNode = NULL;    if (pNode){    pCloneHead = pNode->next;    pCloneNode = pCloneHead;    pNode->next = pCloneNode->next;    pNode = pNode->next;    }    while (pNode){    pCloneNode->next = pNode->next;    pCloneNode = pCloneNode->next;    pNode->next = pCloneNode->next;    pNode = pNode->next;    }    return pCloneHead;    }};