LeetCode 솔루션

[5/5] 225. Implement Stack using Queues

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작성일 2022.05.04 17:20

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[LeetCode 시즌 3] 2022년 5월 5일 문제입니다.

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

[Easy] 225. Implement Stack using Queues

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.

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

Constraints:

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.

Follow-up: Can you implement the stack using only one queue?

#LeetCode, #Bloomberg, #Amazon, #Paypal, #Stack, #Design, #Queue

링크

https://leetcode.com/problems/implement-stack-using-queues/ 1911 회 연결

익명
작성일 2022.05.04 17:31

C++
Runtime: 0 ms, faster than 100.00% of C++ online submissions for Implement Stack using Queues.
Memory Usage: 6.7 MB, less than 88.02% of C++ online submissions for Implement Stack using Queues.

class MyStack {
private:
    queue<int> q;
    
public:
    MyStack() {
        
    }
    
    void push(int x) {
        q.push(x);
    }
    
    int pop() {
        int n = q.size();
        
        for (int i = 0; i < n - 1; ++i) {
            q.push(q.front()); q.pop();
        }
        int res = q.front(); q.pop();
        return res;
    }
    
    int top() {
        int n = q.size();
        int res = 0;
        
        for (int i = 0; i < n; ++i) {
            res = q.front(); q.pop();
            q.push(res);
        }
        return res;
    }
    
    bool empty() {
        return q.empty();
    }
};

익명
작성일 2022.05.05 01:37

class MyStack {
public:
    MyStack() {
        
    }
    
    void push(int x) {
        q1.emplace(x);
    }
    
    int pop() {
        while(q1.size() > 1) {
            q2.emplace(q1.front());
            q1.pop();
        }
        int ret = q1.front();
        q1.pop();
        swap(q1, q2);
        return ret;        
    }
    
    int top() {
        while(q1.size() > 1) {
            q2.emplace(q1.front());
            q1.pop();
        }
        int ret = q1.front();
        q1.pop();
        q2.emplace(ret);
        swap(q1, q2);
        return ret;        
    }
    
    bool empty() {
        return q1.empty();
    }
    queue<int> q1;
    queue<int> q2;
};

익명
작성일 2022.05.05 10:16

Runtime: 65 ms, faster than 5.63% of Python3 online submissions for Implement Stack using Queues.
Memory Usage: 14.1 MB, less than 27.76% of Python3 online submissions for Implement Stack using Queues.

class MyStack:

    def __init__(self):
        self.queue = collections.deque()
        self.temp = collections.deque()

    def push(self, x: int) -> None:
        if self.empty():
            self.queue.append(x)
        else:
            while self.queue:
                self.temp.append(self.queue.popleft())
            self.queue.append(x)
            while self.temp:
                self.queue.append(self.temp.popleft())

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

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

    def empty(self) -> bool:
        if len(self.queue) == 0:
            return True
        else:
            return False