[Leet Code] 225. Implement Stack using Queues

Implement Stack using Queues

 

 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

 

Example 1:

Input
["MyStack", "push", "push", "top", "pop", "empty"]
[[], [1], [2], [], [], []]
Output
[null, null, null, 2, 2, false]
 
Explanation
MyStack myStack = new MyStack();
myStack.push(1);
myStack.push(2);
myStack.top(); // return 2
myStack.pop(); // return 2
myStack.empty(); // return False

 Python 코드

 

Python code 

class MyStack:
 
    def __init__(self):
        self.q = deque()
 
    def push(self, x: int) -> None:
        self.q.append(x)
 
    def pop(self) -> int:
        for i in range(len(self.q) - 1):
            self.push(self.q.popleft())
        return self.q.popleft()
 
    def top(self) -> int:
        return self.q[-1]
 
    def empty(self) -> bool:
        return len(self.q) == 0
 
# Your MyStack object will be instantiated and called as such:
# obj = MyStack()
# obj.push(x)
# param_2 = obj.pop()
# param_3 = obj.top()
# param_4 = obj.empty()

* 참고 링크 : https://www.youtube.com/watch?v=rW4vm0-DLYc 

 

 C++ 코드

 

C ++ code

class MyStack {
    queue<int>q;
public:
    /** Initialize your data structure here. */
    MyStack() {
        
    }
    
    /** 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());
            q.pop();
        }        
    }
    
    /** Removes the element on top of the stack and returns that element. */
    int pop() 
    {
        int result=q.front();
        q.pop();
        return result;
    }
    
    /** Get the top element. */
    int top() 
    {
        return q.front();
    }
    
    /** Returns whether the stack is empty. */
    bool empty() 
    {
        return q.empty();
    }
};
 
/**
 * 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();
 * bool param_4 = obj.empty();
 */

* 참고 링크 : https://github.com/wisdompeak/LeetCode/blob/master/Stack/225.Implement-Stack-using-Queues/225.Implement%20Stack%20using%20Queues.cpp

 

 출처

 

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