1472.Design Browser History
===
###### tags: `Medium`,`Array`,`Linked List`,`Stack`
[1472. Design Browser History](https://leetcode.com/problems/design-browser-history/)
### 題目描述
You have a **browser** of one tab where you start on the `homepage` and you can visit another `url`, get back in the history number of `steps` or move forward in the history number of `steps`.
Implement the `BrowserHistory` class:
* `BrowserHistory(string homepage)` Initializes the object with the `homepage` of the browser.
* `void visit(string url)` Visits `url` from the current page. It clears up all the forward history.
* `string back(int steps)` Move `steps` back in history. If you can only return `x` steps in the history and `steps > x`, you will return only `x` steps. Return the current `url` after moving back in history **at most** `steps`.
* `string forward(int steps)` Move `steps` forward in history. If you can only forward `x` steps in the history and `steps > x`, you will forward only `x` steps. Return the current `url` after forwarding in history **at most** `steps`.
### 範例
**Example 1:**
```
Input:
["BrowserHistory","visit","visit","visit","back","back","forward","visit","forward","back","back"]
[["leetcode.com"],["google.com"],["facebook.com"],["youtube.com"],[1],[1],[1],["linkedin.com"],[2],[2],[7]]
Output:
[null,null,null,null,"facebook.com","google.com","facebook.com",null,"linkedin.com","google.com","leetcode.com"]
Explanation:
BrowserHistory browserHistory = new BrowserHistory("leetcode.com");
browserHistory.visit("google.com"); // You are in "leetcode.com". Visit "google.com"
browserHistory.visit("facebook.com"); // You are in "google.com". Visit "facebook.com"
browserHistory.visit("youtube.com"); // You are in "facebook.com". Visit "youtube.com"
browserHistory.back(1); // You are in "youtube.com", move back to "facebook.com" return "facebook.com"
browserHistory.back(1); // You are in "facebook.com", move back to "google.com" return "google.com"
browserHistory.forward(1); // You are in "google.com", move forward to "facebook.com" return "facebook.com"
browserHistory.visit("linkedin.com"); // You are in "facebook.com". Visit "linkedin.com"
browserHistory.forward(2); // You are in "linkedin.com", you cannot move forward any steps.
browserHistory.back(2); // You are in "linkedin.com", move back two steps to "facebook.com" then to "google.com". return "google.com"
browserHistory.back(7); // You are in "google.com", you can move back only one step to "leetcode.com". return "leetcode.com"
```
**Constraints**:
* 1 <= `homepage.length` <= 20
* 1 <= `url.length` <= 20
* 1 <= `steps` <= 100
* `homepage` and `url` consist of '.' or lower case English letters.
* At most `5000` calls will be made to `visit`, `back`, and `forward`.
### 解答
#### Python
```python=
class BrowserHistory:
def __init__(self, homepage: str):
self.history = [homepage]
self.cur = 0
def visit(self, url: str) -> None:
self.cur += 1
self.history = self.history[:self.cur] + [url]
def back(self, steps: int) -> str:
self.cur = max(0, self.cur - steps)
return self.history[self.cur]
def forward(self, steps: int) -> str:
self.cur = min(len(self.history) - 1, self.cur + steps)
return self.history[self.cur]
```
> [name=Yen-Chi Chen][time=Sat, Mar 18, 2023]
### Reference
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