# 138. Copy List with Random Pointer
## 1.問題
* 一個linked list中每個node除了next之外, 有個random指針會隨機指向list中的任一node, 回傳這個list的deep copy
## 2.想法
* 提問
* function header, parameter
* test input
* 觀察
* 用map儲存已經複製過的node, 避免重複拷貝, 重複走訪
* 說明想法
* 測試計算複雜度
## **3.程式碼**
```
/**
* 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) {
unordered_map m;
return getCopyNode(head, m);
}
private:
RandomListNode * getCopyNode(RandomListNode *head, unordered_map& m) {
if (!head) {
return NULL;
}
if (m.find(head) != m.end()) {
return m[head];
}
RandomListNode * node = new RandomListNode(head->label);
m[head] = node;
node->next = getCopyNode(head->next, m);
node->random = getCopyNode(head->random, m);
return node;
}
};
```
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