【牛客网】copy-list-with-random-pointer题解

题目

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.

分析

题目要求返回链表的深度拷贝，意在要求得到的新链表中的随机指针指向关系要与原链表中一致。因此，该题的关键在于，如何记录原链表中random pointer的指向关系，并在新链表中体现。

代码

1.常规思路：利用map存储原链表node和新链表node的对应关系

/** * 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) return NULL;        map<RandomListNode*, RandomListNode*> source_2_copy;  //记录node对应关系        source_2_copy.insert(make_pair((RandomListNode*)NULL,(RandomListNode*)NULL));   //random pointer为NULL        RandomListNode *copy_head=new RandomListNode(head->label);        source_2_copy.insert(make_pair(head,copy_head));        RandomListNode *p_copy=copy_head;        RandomListNode *p_source=head->next;        //链表复制        while(p_source){            p_copy->next=new RandomListNode(p_source->label);            source_2_copy.insert(make_pair(p_source,p_copy->next));            p_copy=p_copy->next;            p_source=p_source->next;        }        p_source=head;        p_copy=copy_head;        //random pointer复制        while(p_source){            p_copy->random=(source_2_copy.find(p_source->random))->second;            p_source=p_source->next;            p_copy=p_copy->next;        }        return copy_head;    }};

2.Bright Way：在原链表上为每个node new一个副本，然后拆分原链表，同时修改random pointer。（此方法会破坏原链表）

/** * 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) return NULL;        RandomListNode *p=head;        //copy node        while(p){            RandomListNode *copy=new RandomListNode(p->label);            copy->next=p->next;            copy->random=p->random;            p->next=copy;            p=p->next->next;        }        p=head->next;        //get new list        while(p){            if(p->next)                p->next=p->next->next;            if(p->random)                p->random=p->random->next;            p=p->next;        }        return head->next;    }};