1472. Design Browser History

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1472. Design Browser History

Description

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 homepageof the browser.
  • void visit(string url)Visitsurl 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 willreturn only x steps. Return the current urlafter 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 willforward onlyx steps. Return the current urlafter forwarding in history at most steps.

Example:

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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]]
<b>Output:</b>
[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 5000calls will be made to visit, back, and forward.

Hints/Notes

Solution

Language: C++

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class BrowserHistory {
public:
    struct Node {
        Node(string url) : url(url), prev(nullptr), next(nullptr) {}
        string url;
        Node* prev;
        Node* next;
    };

    Node* head;
    Node* current;

    BrowserHistory(string homepage) {
        head = new Node(homepage);
        current = head;
    }

    void visit(string url) {
        Node* nxt = current->next;
        while (nxt) {
            Node* prev = nxt;
            nxt = nxt->next;
            delete(prev);
        }
        Node* node = new Node(url);
        current->next = node;
        node->prev = current;
        current = current->next;
    }

    string back(int steps) {
        while (steps > 0 && current->prev) {
            current = current->prev;
            steps--;
        }
        return current->url;
    }

    string forward(int steps) {
        while (steps > 0 && current->next) {
            current = current->next;
            steps--;
        }
        return current->url;
    }
};

/**
 * Your BrowserHistory object will be instantiated and called as such:
 * BrowserHistory* obj = new BrowserHistory(homepage);
 * obj->visit(url);
 * string param_2 = obj->back(steps);
 * string param_3 = obj->forward(steps);
 */