LintCode复制带随机指针的链表

用了一个哈希表，空间换取时间

/**
 * 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:
    /**
     * @param head: The head of linked list with a random pointer.
     * @return: A new head of a deep copy of the list.
     */
    RandomListNode *copyRandomList(RandomListNode *head) {
        // write your code here
        if(head == nullptr) {
            return nullptr;
        }
        RandomListNode * fhead = head;
        map<RandomListNode*,RandomListNode*> m;
        RandomListNode *p = new RandomListNode(head->label);
        m.insert(pair<RandomListNode*,RandomListNode*>(head,p));
        head = head->next;
        RandomListNode *root = p;
        while (head!=nullptr) {
            p->next = new RandomListNode(head->label);
            p = p->next;
            m.insert(pair<RandomListNode*,RandomListNode*>(head,p));
            head = head->next;
        }
        p = root;
        map<RandomListNode*, RandomListNode*>::iterator iter;  
       while (fhead!=nullptr) {
           if(fhead->random != nullptr) {
              iter = m.find(fhead->random);
              p->random = iter->second;   
           }
            p=p->next;
           fhead = fhead->next;
       }
        
    return root;
    }
};