919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127

class Deque {
    constructor(size) {
        this.size = size;                // max capacity of deque
        this.array = new Array(size);    // array to store elements
        this.front = -1;                 // index of front element
        this.rear = -1;                  // index of rear element
    }

    // Check if deque is full
    isFull() {
        // Case 1: front at 0 and rear at last index
        // Case 2: front is right after rear (circular)
        return (this.front === 0 && this.rear === this.size - 1) || 
               (this.front === (this.rear + 1) % this.size);
    }

    // Check if deque is empty
    isEmpty() {
        return this.front === -1;
    }

    // Insert element at rear
    insertRear(element) {
        if (this.isFull()) {
            console.log("Overflow");
            return;
        }

        // If empty, initialize front and rear
        if (this.front === -1) {
            this.front = 0;
            this.rear = 0;
        } else {
            // Move rear circularly
            this.rear = (this.rear + 1) % this.size;
        }
        this.array[this.rear] = element;
    }

    // Insert element at front
    insertFront(element) {
        if (this.isFull()) {
            console.log("Overflow");
            return;
        }

        // If empty, initialize front and rear
        if (this.front === -1) {
            this.front = 0;
            this.rear = 0;
        } else {
            // Move front circularly backwards
            this.front = (this.front - 1 + this.size) % this.size;
        }
        this.array[this.front] = element;
    }

    // Delete element at front
    deleteFront() {
        if (this.isEmpty()) {
            console.log("Underflow");
            return;
        }

        // Single element case -> reset to empty
        if (this.front === this.rear) {
            this.front = -1;
            this.rear = -1;
        } else {
            // Move front circularly forward
            this.front = (this.front + 1) % this.size;
        }
    }

    // Delete element at rear
    deleteRear() {
        if (this.isEmpty()) {
            console.log("Underflow");
            return;
        }

        // Single element case -> reset to empty
        if (this.front === this.rear) {
            this.front = -1;
            this.rear = -1;
        } else {
            // Move rear circularly backwards
            this.rear = (this.rear - 1 + this.size) % this.size;
        }
    }

    // Get front element
    getFront() {
        if (this.isEmpty()) {
            console.log("Underflow");
            return -1;
        }
        return this.array[this.front];
    }

    // Get rear element
    getRear() {
        if (this.isEmpty()) {
            console.log("Underflow");
            return -1;
        }
        return this.array[this.rear];
    }
}

// Driver
const dq = new Deque(10);

dq.insertFront(10);
console.log("Front:", dq.getFront());

dq.insertRear(20);
dq.insertRear(30);
console.log("Rear:", dq.getRear());

dq.deleteFront();
console.log("Front after deletion:", dq.getFront());

dq.deleteRear();
console.log("Rear after deletion:", dq.getRear());
Time Complexity: O(1) for all operations (insertFront, insertRear, deleteFront, deleteRear, getFront, getRear, isFull, isEmpty). Each operation involves only index calcu