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Queue Design

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225. Implement Stack using Queues

225. Implement Stack using Queues - Python Solution
from collections import deque


# Queue
class MyStack:

    def __init__(self):
        self.q1 = deque()  # main queue
        self.q2 = deque()  # auxiliary queue

    def push(self, x: int) -> None:
        self.q1.append(x)

    def pop(self) -> int:
        while len(self.q1) > 1:
            self.q2.append(self.q1.popleft())
        res = self.q1.popleft()
        self.q1, self.q2 = self.q2, self.q1
        return res

    def top(self) -> int:
        while len(self.q1) > 1:
            self.q2.append(self.q1.popleft())
        res = self.q1[0]
        self.q2.append(self.q1.popleft())
        self.q1, self.q2 = self.q2, self.q1
        return res

    def empty(self) -> bool:
        return not self.q1


obj = MyStack()
obj.push(1)
obj.push(2)
obj.push(3)
obj.push(4)
print(obj.pop())  # 4
print(obj.top())  # 3
print(obj.empty())  # False
print(obj.pop())  # 3

232. Implement Queue using Stacks

  • LeetCode | LeetCode CH (Easy)

  • Tags: stack, design, queue

  • Implement the following operations of a queue using stacks.
    • push(x) - Push element x to the back of queue.
    • pop() - Removes the element from in front of queue.
    • peek() - Get the front element.
    • empty() - Return whether the queue is empty.
232. Implement Queue using Stacks - Python Solution
class MyQueue:
    def __init__(self):
        self.stack_in = []
        self.stack_out = []

    def push(self, x: int) -> None:
        self.stack_in.append(x)

    def pop(self) -> int:
        if self.empty():
            return None

        if self.stack_out:
            return self.stack_out.pop()
        else:
            for _ in range(len(self.stack_in)):
                self.stack_out.append(self.stack_in.pop())
            return self.stack_out.pop()

    def peek(self) -> int:
        answer = self.pop()
        self.stack_out.append(answer)
        return answer

    def empty(self) -> bool:
        return not (self.stack_in or self.stack_out)


obj = MyQueue()
obj.push(1)
print(obj.pop())  # 1
print(obj.peek())  # None
print(obj.empty())  # False

622. Design Circular Queue

622. Design Circular Queue - Python Solution
# Design
class MyCircularQueue:

    def __init__(self, k: int):
        self.queue = [0] * k
        self.head = 0
        self.tail = -1
        self.size = 0
        self.capacity = k

    def enQueue(self, value: int) -> bool:
        if self.isFull():
            return False
        self.tail = (self.tail + 1) % self.capacity
        self.queue[self.tail] = value
        self.size += 1
        return True

    def deQueue(self) -> bool:
        if self.isEmpty():
            return False
        self.head = (self.head + 1) % self.capacity
        self.size -= 1
        return True

    def Front(self) -> int:
        if self.isEmpty():
            return -1
        return self.queue[self.head]

    def Rear(self) -> int:
        if self.isEmpty():
            return -1
        return self.queue[self.tail]

    def isEmpty(self) -> bool:
        return self.size == 0

    def isFull(self) -> bool:
        return self.size == self.capacity


obj = MyCircularQueue(3)
print(obj.enQueue(1))  # True
print(obj.enQueue(2))  # True
print(obj.enQueue(3))  # True
print(obj.enQueue(4))  # False
print(obj.Rear())  # 3
print(obj.isFull())  # True
print(obj.deQueue())  # True

641. Design Circular Deque

1670. Design Front Middle Back Queue

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