Implement Stack using Queues

Desicription

Implement the following operations of a stack using queues.

  • push(x) – Push element x onto stack.
  • pop() – Removes the element on top of the stack.
  • top() – Get the top element.
  • empty() – Return whether the stack is empty.

Example:

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MyStack stack = new MyStack();
stack.push(1);
stack.push(2);
stack.top(); // returns 2
stack.pop(); // returns 2
stack.empty(); // returns false

Notes:

  • You must use only standard operations of a queue – which means only push to back, peek/pop from front, size, and is empty operations are valid.

  • Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.

  • You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

Solution

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/**
* Your MyStack object will be instantiated and called as such:
* MyStack obj = new MyStack();
* obj.push(x);
* int param_2 = obj.pop();
* int param_3 = obj.top();
* bool param_4 = obj.empty();
*/
class MyStack {
public:
queue<int> q;
/** Initialize your data structure here. */
MyStack() {
}
/** Push element x onto stack. */
void push(int x) {
q.push(x);
for(int i = 1; i < q.size(); i++) {
q.push(q.front());
q.pop();
}
}
/** Removes the element on top of the stack and returns that element. */
int pop() {
int result = q.front();
q.pop();
return result;
}
/** Get the top element. */
int top() {
return q.front();
}
/** Returns whether the stack is empty. */
bool empty() {
return q.empty();
}
};