Implement Queue using Stacks

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
onlystandard 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).

Use stack.

Push – o(1)

pop – o(n)

peek – o(1)

empty – o(1)

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