1 minute read

225. Implement Stack using Queues

문제 링크

https://leetcode.com/problems/implement-stack-using-queues/description/

문제 설명

Implement a last-in-first-out (LIFO) stack using only two queues. The implemented stack should support all the functions of a normal stack (push, top, pop, and empty).

Implement the MyStack class:

  • void push(int x) Pushes element x to the top of the stack.
  • int pop() Removes the element on the top of the stack and returns it.
  • int top() Returns the element on the top of the stack.
  • boolean empty() Returns true if the stack is empty, false otherwise.

Notes:

  • You must use only standard operations of a queue, which means that only push to back, peek/pop from front, size and is empty operations are valid.
  • Depending on your language, the queue may not be supported natively. You may simulate a queue using a list or deque (double-ended queue) as long as you use only a queue’s standard operations.

제한 사항

  • 1 <= x <= 9
  • At most 100 calls will be made to push, pop, top, and empty.
  • All the calls to pop and top are valid.

입출력 예 #1

  1. Input : [“MyStack”, “push”, “push”, “top”, “pop”, “empty”] [[], [1], [2], [], [], []]
  2. Output : [null, null, null, 2, 2, false]
  3. Explanation MyStack myStack = new MyStack();

myStack.push(1);

myStack.push(2);

myStack.top(); // return 2

myStack.pop(); // return 2

myStack.empty(); // return False

문제 풀이

que를 이용한 stack 구현이기에 push 동작에 유의하며 작성한다.

class MyStack:
    def __init__(self):
        self.q = collections.deque()

    def push(self, x: int) -> None:
        self.q.append(x)
        # 요소 삽입 후 맨 앞에 두는 상태로 재정렬
        for _ in range(len(self.q) - 1):
            self.q.append(self.q.popleft())

    def pop(self) -> int:
        return self.q.popleft()

    def top(self) -> int:
        return self.q[0]

    def empty(self) -> bool:
        return len(self.q) == 0

Comments

You May Also Enjoy