leetcode 138. 复制带随机指针的链表

C++采用哈希表，时间复杂度O(n),空间复杂度O(n)空间复杂度应该可以降低；

/*
// Definition for a Node.
class Node {
public:
    int val;
    Node* next;
    Node* random;

    Node() {}

    Node(int _val, Node* _next, Node* _random) {
        val = _val;
        next = _next;
        random = _random;
    }
};
*/
class Solution {
public:
    Node* copyRandomList(Node* head) {
        //建立哈希表遍历两次，一次复制next并填充哈希表，第二次复制random
        unordered_map<Node*,Node*> h;
        Node *pre, *cur, *root;
        pre=root=new Node(-1,NULL,NULL);
        cur=head;
        while(cur!=NULL){
            int v=cur->val;
            Node *p=new Node(v,NULL,NULL);
            h[cur]=p;
            pre->next=p;
            pre=p;
            cur=cur->next;
        }
        cur=root->next;
        pre=head;
        h[NULL]=NULL;
        while(cur!=NULL){
            cur->random=h[pre->random];
            cur=cur->next;
            pre=pre->next;
        }
        return root->next;
    }
};