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Implement a Deque using a List

CodeWithML
Sharing solutions to coding problems.
Originally published at codewithml.netlify.app ・3 min read

Problem Statement: Implement a Deque with all it's functions using a List.

A Deque is a double ended queue, where elements can be added from both the ends of the queue.

Functions to be implemented

  1. addRear
  2. addFront
  3. getRear
  4. getFront
  5. deleteRear
  6. deleteFront
  7. isEmpty
  8. Size

Test Cases

  1. addRear
    • Add element at the rear of deque on an empty deque.
    • Add element at the rear of deque on a non-empty deque.
  2. addFront
    • Add element at the front of deque on an empty deque.
    • Add element at the front of deque on a non-empty deque.
  3. getRear
    • Get element from the rear of deque on an empty deque --> None.
    • Get element from the rear of deque on a non-empty deque --> value.
  4. getFront
    • Get element from the front of deque on an empty deque --> None.
    • Get element from the front of deque on a non-empty deque --> value.
  5. deleteRear
    • Delete element from the rear of deque on an empty deque --> None.
    • Delete element from the rear of deque on a non-empty deque --> value.
  6. deleteFront
    • Delete element from the front of deque on an empty deque --> None.
    • Delete element from the front of deque on a non-empty deque --> value.
  7. isEmpty
    • isEmpty on an non-empty deque --> True.
    • isEmpty on a empty deque --> False.
  8. Size
    • size on an non-empty deque --> None.
    • size on a empty deque --> value.

Algorithm

  1. addRear
    • Insert the element at the first index of list.
  2. addFront
    • Insert the element at the last index of list.
  3. getRear
    • If deque is empty,
      • return None.
    • Else,
      • Get the element present at the first index of list.
  4. getFront
    • If deque is empty,
      • return None.
    • Else,
      • Get the element present at the last index of list.
  5. deleteRear
    • If deque is empty,
      • return None.
    • Else,
      • remove the element at the first index of list.
  6. deleteFront
    • If deque is empty,
      • return None.
    • Else,
      • remove the element at the last index of list.
  7. isEmpty
    • If list is empty,
      • return True.
    • Else,
      • return False.
  8. Size
    • Return the length of the list.

Time and Space complexity

  1. addFront
    • Time complexity: Best case - O(1), Worst case - O(n)
    • Space complexity: O(1)
  2. addRear
    • Time complexity: Best case - O(1), Worst case - O(n)
    • Space complexity: O(1)
  3. getFront
    • Time complexity: O(1)
    • Space complexity: O(1)
  4. getRear
    • Time complexity: O(1)
    • Space complexity: O(1)
  5. deleteFront
    • Time complexity: O(1)
    • Space complexity: O(1)
  6. deleteRear
    • Time complexity: O(1)
    • Space complexity: O(1)
  7. isEmpty
    • Time complexity: O(1)
    • Space complexity: O(1)
  8. Size
    • Time complexity: O(1)
    • Space complexity: O(1)

Code

class Deque(object):
    def __init__(self):
        self.deque = []

    def isEmpty(self):
        return self.deque == []

    def addRear(self, data):
        self.deque.insert(0, data)

    def addFront(self, data):
        self.deque.append(data)

    def getRear(self):
        if self.isEmpty():
            return None
        return self.deque[0]

    def getFront(self):
        if self.isEmpty():
            return None
        return self.deque[-1]

    def removeRear(self):
        if self.isEmpty():
            return None
        return self.deque.pop(0)

    def removeFront(self):
        if self.isEmpty():
            return None
        return self.deque.pop()

    def size(self):
        return len(self.deque)

Unit Test

import unittest
from deque import Deque


class TestDeque(unittest.TestCase):
    def testDeque(self):
        print('Test: Empty Deque')
        deque = Deque()
        self.assertEqual(deque.size(), 0)
        self.assertEqual(deque.getFront(), None)
        self.assertEqual(deque.getRear(), None)
        self.assertEqual(deque.removeFront(), None)
        self.assertEqual(deque.removeRear(), None)
        self.assertEqual(deque.isEmpty(), True)

        print('Test: One element')
        deque = Deque()
        deque.addFront(5)
        self.assertEqual(deque.size(), 1)
        self.assertEqual(deque.getFront(), 5)
        self.assertEqual(deque.removeFront(), 5)
        self.assertEqual(deque.isEmpty(), True)
        deque.addRear(5)
        self.assertEqual(deque.isEmpty(), False)
        self.assertEqual(deque.size(), 1)
        self.assertEqual(deque.getRear(), 5)
        self.assertEqual(deque.removeRear(), 5)
        self.assertEqual(deque.isEmpty(), True)

        print('Test: Multiple elements')
        deque = Deque()
        deque.addFront(1)
        deque.addRear(3)
        deque.addFront(2)
        deque.addRear(4)
        self.assertEqual(deque.size(), 4)
        self.assertEqual(deque.getFront(), 2)
        self.assertEqual(deque.removeFront(), 2)
        self.assertEqual(deque.size(), 3)
        self.assertEqual(deque.removeRear(), 4)
        self.assertEqual(deque.getRear(), 3)
        self.assertEqual(deque.size(), 2)
        self.assertEqual(deque.isEmpty(), False)
        self.assertEqual(deque.removeFront(), 1)
        self.assertEqual(deque.removeRear(), 3)
        self.assertEqual(deque.isEmpty(), True)
        print('Success: testDeque')


def main():
    test = TestDeque()
    test.testDeque()


if __name__ == "__main__":
    main()


Github repo

Happy Coding !!!

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