225. Implement Stack using Queues
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
, andis 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 { List<Integer> list; /** Initialize your data structure here. */ public MyStack() { list = new ArrayList<>(); } /** Push element x onto stack. */ public void push(int x) { list.add(x); } /** Removes the element on top of the stack and returns that element. */ public int pop() { return list.remove(list.size()-1); } /** Get the top element. */ public int top() { return list.get(list.size()-1); } /** Returns whether the stack is empty. */ public boolean empty() { return list.size() == 0; } } /** * 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(); * boolean param_4 = obj.empty(); */
[문제] https://leetcode.com/problems/implement-stack-using-queues/
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