题目描述：
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.
Notes:
- You must use only standard operations of a queue -- which means only
push to back,peek/pop from front,size, andis 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).
解题思路：
代码如下：
class MyStack {
Queue<Integer> queue = new LinkedList<Integer>();
// Push element x onto stack.
public void push(int x) {
queue.offer(x);
}
// Removes the element on top of the stack.
public void pop() {
int size = queue.size();
for(int i = 1; i < size; i++)
queue.offer(queue.poll());
queue.poll();
}
// Get the top element.
public int top() {
int size = queue.size();
for(int i = 1; i < size; i++)
queue.offer(queue.poll());
int head = queue.poll();
queue.offer(head);
return head;
}
// Return whether the stack is empty.
public boolean empty() {
return queue.isEmpty();
}
}