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:
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).
public class MyStack {
Queue<int> queue1;
Queue<int> queue2;
/** Initialize your data structure here. */
public MyStack() {
queue1 = new Queue<int>();
queue2 = new Queue<int>();
}
/** Push element x onto stack. */
public void Push(int x) {
queue2.Enqueue(x);
while(queue1.Count>0){
queue2.Enqueue(queue1.Dequeue());
}
Queue<int> temp = queue1;
queue1 = queue2;
queue2 = temp;
}
/** Removes the element on top of the stack and returns that element. */
public int Pop() {
if(queue1.Count<1){
return -1;
}
return queue1.Dequeue();
}
/** Get the top element. */
public int Top() {
if(queue1.Count<1){
return -1;
}
return queue1.Peek();
}
/** Returns whether the stack is empty. */
public bool Empty() {
return queue1.Count()<1;
}
}
/**
* 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();
*/Time Complexity: O(n)
Space Complexity: O(n)
