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, 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).
class MyStack {
public:
std::queue<int>q;
/** Push element x onto stack. */
void push(int x) {
q.push(x);
for(int i=0;i<q.size()-1;++i)
{
q.push(q.front());//本题题解的核心语句,注意揣摩
q.pop();
}
}
/** Removes the element on top of the stack and returns that element. */
int pop() {
int t = q.front();
q.pop();
return t;
}
/** Get the top element. */
int top() {
return q.front();
}
/** Returns whether the stack is empty. */
bool empty() {
return q.empty();
}
};