g1401_1500.s1472_design_browser_history.BrowserHistory Maven / Gradle / Ivy

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package g1401_1500.s1472_design_browser_history;

// #Medium #Array #Stack #Design #Linked_List #Data_Stream #Doubly_Linked_List
// #2022_03_29_Time_76_ms_(82.33%)_Space_86.4_MB_(14.42%)

/**
 * 1472 - Design Browser History\.
 *
 * Medium
 *
 * 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`.
 *
 * **Example:**
 *
 * **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`.
**/
public class BrowserHistory {

    static class Node {
        Node prev;
        Node next;
        String url;

        Node(String url) {
            this.url = url;
            this.prev = null;
            this.next = null;
        }
    }

    private Node curr;

    public BrowserHistory(String homepage) {
        curr = new Node(homepage);
    }

    public void visit(String url) {
        Node newNode = new Node(url);
        curr.next = newNode;
        newNode.prev = curr;
        curr = curr.next;
    }

    public String back(int steps) {
        while (curr.prev != null && steps-- > 0) {
            curr = curr.prev;
        }
        return curr.url;
    }

    public String forward(int steps) {
        while (curr.next != null && steps-- > 0) {
            curr = curr.next;
        }
        return curr.url;
    }
}