LeetCode-Implement Queue using Stacks

Posted 2020-07-12 IncredibleThings

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).

class MyQueue {
    Stack<Integer> inStack=new Stack<Integer>();
    Stack<Integer> outStack=new Stack<Integer>();
    // Push element x to the back of queue.
    public void push(int x) {
        inStack.push(x);
    }

    // Removes the element from in front of queue.
    public void pop() {
        
        if(!outStack.empty()){
            outStack.pop();
        }
        
        else{
            while(!inStack.empty()){
                int value=inStack.pop();
                outStack.push(value);
            }
            outStack.pop();
        }
        

    }

    // Get the front element.
    public int peek() {
        int res=0;
        if(!outStack.empty()){
            res=outStack.peek();
        }
        else{
            while(!inStack.empty()){
                int value=inStack.pop();
                outStack.push(value);
            }
            res=outStack.peek();
        }
        return res;
    }

    // Return whether the queue is empty.
    public boolean empty() {
        if(inStack.empty() && outStack.empty()){
            return true;
        }
        return false;
    }
}