dequeue.ts

class Dequeue() {
    /**
        Construct a dequeue of the form:

        B                   F
        ---------------------
        e/d               e/d 
        ---------------------
     */
    private queue: number[];
    constructor() {
        this.queue = [];
    }
    enqueueFront(v: number): void { // O(1)
        this.queue.push(v);
    }

    enqueueBack(v: number): void { // O(1)
        this.queue = [v].concat(this.queue);
    }

    dequeueFront(): number { // O(1)
        return this.queue.pop();
    }

    dequeueBack(): number { // O(n)
        this.queue.reverse();
        let d = this.queue.pop();
        this.queue.reverse();
        return d;
    }

    peekBack(): number { // O(1)
        return this.queue.at(0)
    }

    peekFront(): number { // O(1)
        return this.queue.at(-1);
    }
}