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 [回到題目列表](https://hackmd.io/@Marsgoat/leetcode_every_day)