**Difficulty: Easy**

**Frequency: N/A**

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).

**My solution:**

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**Code:**

class Queue { public: // Push element x to the back of queue. void push(int x) { stack<int> tmp; while (!s.empty()) { tmp.push(s.top()); s.pop(); } s.push(x); while (!tmp.empty()) { s.push(tmp.top()); tmp.pop(); } } // Removes the element from in front of queue. void pop(void) { s.pop(); } // Get the front element. int peek(void) { return s.top(); } // Return whether the queue is empty. bool empty(void) { return s.empty(); } private: stack<int> s; };

**Another solution:**

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**Things to learn:**