LeetCode 题解（88）: Copy List with Random Pointer

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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.

题解：

两种做法：一种O(1) space in place copy，一种HashTable 额外O(n) space copy。

C++做法一：

class Solution {public:    RandomListNode *copyRandomList(RandomListNode *head) {        if(!head)            return NULL;        RandomListNode *p = head;        while(p != NULL) {            RandomListNode *newNode = new RandomListNode(p->label);            newNode->next = p->next;            p->next = newNode;            p = p->next->next;        }                p = head;        while(p != NULL) {            if(p->random != NULL)                p->next->random = p->random->next;            p = p->next->next;        }                RandomListNode *newHead = head->next;        p = head;        RandomListNode *q = head->next;                while(p != NULL) {            p->next = q->next;            if(q->next != NULL)                q->next = q->next->next;            p = p->next;            if(p != NULL)                q = p->next;        }        return newHead;            }};

C++做法二：

class Solution {public:    RandomListNode *copyRandomList(RandomListNode *head) {        if(!head)            return NULL;        unordered_map<RandomListNode*, RandomListNode*> nodeToNode;        RandomListNode *p = head;        RandomListNode *newListHead = copyNode(p, nodeToNode);        RandomListNode *q = newListHead;        while(q) {            if(head->random != NULL)                q->random = nodeToNode[head->random];            q = q->next;            head = head->next;        }        return newListHead;    }        RandomListNode* copyNode(RandomListNode* head, unordered_map<RandomListNode*, RandomListNode*> & nodeToNode) {        if(!head)            return NULL;        RandomListNode* newHead = new RandomListNode(head->label);        nodeToNode.insert(pair<RandomListNode*, RandomListNode*>(head, newHead));        newHead->next = copyNode(head->next, nodeToNode);        return newHead;    }};

Java做法一：

/** * 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 null;                RandomListNode p = head;        while(p != null) {            RandomListNode newNode = new RandomListNode(p.label);            newNode.next = p.next;            p.next = newNode;            p = p.next.next;        }                p = head;        while(p != null) {            if(p.random != null)                p.next.random = p.random.next;            p = p.next.next;        }                p = head;        RandomListNode newHead = p.next;        while(p != null) {            RandomListNode temp = p.next;            p.next = temp.next;            if(p.next != null)                temp.next = p.next.next;            p = p.next;        }                return newHead;    }}

Python做法二：

# Definition for singly-linked list with a random pointer.# class RandomListNode:#     def __init__(self, x):#         self.label = x#         self.next = None#         self.random = Noneclass Solution:    # @param head, a RandomListNode    # @return a RandomListNode    def copyRandomList(self, head):        if head == None:            return None        d = {}        p = head        newHead = self.copyList(p, d)        p = head        q = newHead        while p != None:            if p.random != None:                q.random = d[p.random]            p = p.next            q = q.next        return newHead            def copyList(self, head, d):        if head == None:            return head                newNode = RandomListNode(head.label)        d[head] = newNode        newNode.next = self.copyList(head.next, d)        return newNode

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