Leetcode Implement Queue using Stacks

Implement the following operations of a queue using stacks.

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

Notes:

• Must use onlyStandard operations of a stack – which means onlypush to top,peek/pop from top,size, andis emptyOperations is valid.
• Depending on your language, stack may is not supported natively. You could simulate a stack by using a list or deque (double-ended queue), as long as if you have standard operations of a s Tack.

• You may assume this all operations is valid (for example, no pop or peek operations would be called on an empty queue).

Thinking Analysis: This question and a few years ago wrote a story by the blog is the same topic: The interview problem study with two stack simulation implementation of the queue. The basic approach is simple, with two stacks can be simulated a queue, the basic idea is two LIFO = FIFO, element into the queue always into a stack, element out of the queue if the B stack is not empty directly eject the B stack head element; If b stack is empty, put a stack of elements out of the stack and then eject the B stack head, This simulates a queue. The core is to ensure that each element is out of the stack through a A-B two stacks, so that the implementation of two LIFO = FIFO first.
AC Code

Class Myqueue {    //Push element x to the back of the queue.    stack<integer> Stacka = new stack<integer> ();    stack<integer> stackb = new stack<integer> ();            public void push (int x) {        stacka.push (x);    }    Removes the element from in front of the queue.    public void Pop () {        if (!stackb.isempty ()) {            stackb.pop ()        } and else {while            (!stacka.isempty ()) {                Stackb.push (Stacka.pop ());            }            Stackb.pop ();        }    }    Get the front element.    public int Peek () {        if (!stackb.isempty ()) {            return Stackb.peek (),        } else {while            (!stacka.isempty ( ) {                Stackb.push (Stacka.pop ());            }            return Stackb.peek ();        }    }    Return whether the queue is empty.    public Boolean empty () {        return (Stacka.isempty () && stackb.isempty ())}    }

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Leetcode Implement Queue using Stacks