363738394041424344454647484950515253545556575859606162636465666768

// Stack implementation using Queue
class QueueStack {
    constructor() {
        // Queue
        this.q = [];
    }

    // Method to push element in the stack
    push(x) {
        // Get size
        let s = this.q.length;
        // Add element
        this.q.push(x);

        // Move elements before new element to back
        for (let i = 0; i < s; i++) {
            this.q.push(this.q.shift());
        }
    }

    // Method to pop element from stack
    pop() {
        // Get front element
        let n = this.q[0];
        // Remove front element
        this.q.shift();
        // Return removed element
        return n;
    }

    // Method to return the top of stack
    top() {
        // Return front element
        return this.q[0];
    }

    // Method to check if the stack is empty
    isEmpty() {
        return this.q.length === 0;
    }
}

const st = new QueueStack();

// List of commands
const commands = ["QueueStack", "push", "push", "pop", "top", "isEmpty"];
const inputs = [[], [4], [8], [], [], []];

for (let i = 0; i < commands.length; ++i) {
    switch (commands[i]) {
        case "push":
            st.push(inputs[i][0]);
            console.log("null ");
            break;
        case "pop":
            console.log(st.pop() + " ");
            break;
        case "top":
            console.log(st.top() + " ");
            break;
        case "isEmpty":
            console.log(st.isEmpty() ? "true " : "false ");
            break;
        case "QueueStack":
            console.log("null ");
            break;
    }
}

Complexity Analysis

Time Complexity:
Push operation: O(n) (where n is the number of elements in the queue at that time) because every time an element is pushed, all the elements in the queue are popped from the front and pushed in the back again.
Pop operation: O(1) as constant operations are performed.
Top operation: O(1) as constant operations are performed.
IsEmpty operation: O(1) as constant operations are performed.

Space Complexity: O(k) for storing k elements in the queue.