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.
You must use only
standard operations of a queue -- which means only
push to back,
peek/pop from front,
is emptyoperations 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).
Update (2015-06-11):The class name of the Java
function had been updated to
instead of Stack.
Special thanks to @jianchao.li.fighter for adding this problem and all test cases.