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# Implement Stack using Queues LeetCode Solution – Queslers

## Problem – Implement Stack using Queues LeetCode Solution

Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (`push``top``pop`, and `empty`).

Implement the `MyStack` class:

• `void push(int x)` Pushes element x to the top of the stack.
• `int pop()` Removes the element on the top of the stack and returns it.
• `int top()` Returns the element on the top of the stack.
• `boolean empty()` Returns `true` if the stack is empty, `false` otherwise.

Notes:

• You must use only standard operations of a queue, which means that only `push to back``peek/pop from front``size` and `is empty` operations are valid.
• Depending on your language, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue’s standard operations.

Example 1:

``````Input
["MyStack", "push", "push", "top", "pop", "empty"]
[[], , , [], [], []]
Output
[null, null, null, 2, 2, false]

Explanation
MyStack myStack = new MyStack();
myStack.push(1);
myStack.push(2);
myStack.top(); // return 2
myStack.pop(); // return 2
myStack.empty(); // return False``````

Constraints:

• `1 <= x <= 9`
• At most `100` calls will be made to `push``pop``top`, and `empty`.
• All the calls to `pop` and `top` are valid.

Follow-up: Can you implement the stack using only one queue?

### Implement Stack using Queues LeetCode Solution in C++

``````class Stack {
queue<int> q;
public:
void push(int x) {
q.push(x);
for (int i=1; i<q.size(); i++) {
q.push(q.front());
q.pop();
}
}

void pop() {
q.pop();
}

int top() {
return q.front();
}

bool empty() {
return q.empty();
}
};
``````

### Implement Stack using Queues LeetCode Solution in Java

``````class MyStack {

private Queue<Integer> queue = new LinkedList<>();

public void push(int x) {
for (int i=1; i<queue.size(); i++)
}

public void pop() {
queue.remove();
}

public int top() {
return queue.peek();
}

public boolean empty() {
return queue.isEmpty();
}
}
``````

### Implement Stack using Queues LeetCode Solution in Python

``````class Stack:

def __init__(self):
self._queue = collections.deque()

def push(self, x):
q = self._queue
q.append(x)
for _ in range(len(q) - 1):
q.append(q.popleft())

def pop(self):
return self._queue.popleft()

def top(self):
return self._queue

def empty(self):
return not len(self._queue)
``````
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