leetcode

0 class BrowserHistory {

1 struct Node {

2 Node *next, *prev;

3 string val;

4 Node(string val = "#", Node *prev = nullptr, Node *next = nullptr)

5 : val(val), prev(prev), next(next) {}

6 };

7 Node *head = nullptr, *tail = nullptr, *crnt = nullptr;

8

9 public:

10 BrowserHistory(string homepage) { crnt = head = tail = new Node(homepage); }

11

12 void visit(string url) {

13 for (Node *t = tail->next; t;) {

14 Node *tmp = t;

15 t = t->next;

16 delete tmp;

17 }

18 crnt = tail = tail->next = new Node(url, tail, nullptr);

19 }

20

21 string back(int steps) {

22 while (steps-- && crnt->prev)

23 tail = crnt = crnt->prev;

24 return crnt->val;

25 }

26

27 string forward(int steps) {

28 while (steps-- && crnt->next)

29 tail = crnt = crnt->next;

30 return crnt->val;

31 }

32 };