Design Browser History

Leetcode Problem 1472: Design Browser History

Problem Summary

Design a browser history system for a single-tab browser. The browser starts on a given homepage. visit(url) navigates to the given URL from the current page, clearing all forward history. back(steps) moves back at most the given number of steps in the history, returning the current URL after moving. If there are fewer pages in the back history than the requested steps, it moves back as far as possible. forward(steps) moves forward at most the given number of steps in the history, returning the current URL after moving. If there are fewer pages in the forward history than the requested steps, it moves forward as far as possible.

Constraints:

• The homepage and all visited URLs are strings between 1 and 20 characters, consisting of lowercase English letters and dots.
• At most 5,000 calls will be made to visit, back, and forward.
• Steps are always at least 1.

Techniques

• Array
• Linked List
• Stack
• Design
• Doubly-Linked List
• Data Stream

Solution

class BrowserHistory {
    constructor(
        homepage: string,
        private currentUrl: string = homepage,
        private backStack: string[] = [], 
        private forwardStack: string[] = []
    ) { }

    visit(url: string): void {
        this.backStack.push(this.currentUrl)
        this.currentUrl = url
        this.forwardStack = []
    }

    back(steps: number): string {
        let currentStep = steps

        while (this.backStack.length > 0 && currentStep > 0) {
            this.forwardStack.push(this.currentUrl)
            this.currentUrl = this.backStack.pop()!
            currentStep--
        }
        
        return this.currentUrl
    }

    forward(steps: number): string {
        let currentStep = steps

        while (this.forwardStack.length > 0 && currentStep > 0) {
            this.backStack.push(this.currentUrl)
            this.currentUrl = this.forwardStack.pop()!
            currentStep--
        }
        
        return this.currentUrl
    }
}