Implement the following operations of a queue using stacks.

• push(x) -- Push element x to the back of queue.
• pop() -- Removes the element from in front of queue.
• peek() -- Get the front element.
• empty() -- Return whether the queue is empty.

Notes:

• You must use only standard operations of a stack -- which means only push to top, peek/pop from top, size, and is empty operations are valid.
• Depending on your language, stack may not be supported natively. You may simulate a stack by using a list or deque (double-ended queue), as long as you use only standard operations of a stack.
• You may assume that all operations are valid (for example, no pop or peek operations will be called on an empty queue).

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1 class MyQueue { 2     Stack
      
        s1 = new Stack
       
        (); 3     Stack
        
          s2 = new Stack
         
          (); 4     // Push element x to the back of queue. 5     public void push(int x) { 6         s1.push(x); 7     } 8  9     // Removes the element from in front of queue.10     public void pop() {11         if(!s2.isEmpty()) s2.pop();12         else{13             while(!s1.isEmpty()) s2.push(s1.pop());14             s2.pop();15         }16     }17 18     // Get the front element.19     public int peek() {20         if(!s2.isEmpty()) return s2.peek();21         else{22             while(!s1.isEmpty()) s2.push(s1.pop());23             return s2.peek();24         }25     }26 27     // Return whether the queue is empty.28     public boolean empty() {29         return s1.isEmpty() && s2.isEmpty();30     }31 }