[LeetCode] 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. 劍指OFFER上的題，中間 head->random 原來有可能是NULL,所以要添加一個判斷，很坑。

/** * 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) {        // Note: The Solution object is instantiated only once and is reused by each test case.        if(!head)            return NULL;        cloneList(head);        cloneRandomPtr(head);        return removeClone(head);    }    void cloneList(RandomListNode* head)    {        while(head)        {            RandomListNode* toAdd=new RandomListNode(head->label);            RandomListNode* pNext=head->next;            toAdd->next=pNext;            head->next=toAdd;            head=pNext;        }    }    void cloneRandomPtr(RandomListNode* head)    {        while(head)        {            if(head->random)                head->next->random=head->random->next;            head=head->next->next;        }    }    RandomListNode* removeClone(RandomListNode* head)    {        RandomListNode guard(-1);        RandomListNode* tail=&guard;        while(head)        {            tail->next=head->next;            tail=tail->next;            head->next=head->next->next;            head=head->next;        }        return guard.next;    }};