Implementation of Dynamic Arrays

When we create a regular array, its size is fixed. For example, if we make an array of length 5, we can add only five items to it, not more. On the other hand, dynamic arrays are resizable, i.e., the size of an array can change in the program. It can be changed by adding new items or removing existing ones. Therefore, we do not need to determine the size ahead of time, we can add elements on the go, and the size of an array will increase automatically.

How to implement Dynamic Arrays?

So, let’s get started and see how we can implement dynamic arrays.

  • Initially, we create an array of a specific capacity, let’s say 2, and it represents our dynamic array. At this time, the size is 0, i.e., from the user’s perspective, the array is empty. However, internally, it is still a fixed-sized array having a temporary capacity of 2. It is temporary because it can change if required.
  • Later on, when the user appends an item, the program checks whether the current size of the dynamic array is equal to its capacity or not. If it is not, then the element gets inserted at this position, and the size gets incremented.
  • If the size is equal to the capacity, then the array gets resized, and the item gets appended in the new resized array.
  • To resize it, we create a new array of an increased capacity, let’s say double the previous one. Then, we copy all the items from the previous array to the new one. This new array represents our dynamic array now.
  • To pop the last item from the array, we decrement the size and return the deleted element.

Consider the following implementation of a dynamic array in Python. It contains the following functionalities.

  • DynamicArray(type) creates a dynamic array of a given type. It supports integer, float, double, and character type.
  • append() inserts an item at the end of an array.
  • pop() removes the last element and returns it.
  • length() returns the size of the array.
  • getItem() returns the item at a given index.

The code

import array

class DynamicArray(object):
    def __init__(self, type):
        self.__capacity = 2  # initial capacity of 2
        self.__size = 0  # size of the array/ index for the next item
        self.__type = type
        self.__array = self.__createArray(
        )  # initially create an array of size 2

    def length(self):  # return length of the array
        return self.__size

    def append(self, item):
        if self.__size == self.__capacity:  # resize array if the capacity is full
            self.__resize(2 * self.__capacity)
        self.__array[self.__size] = item  # append item
        self.__size = 1

    def pop(self):
        if self.__size == 0:
            raise Exception("Array is empty")
        self.__size -= 1  #
        item = self.__array[self.__size]
        return item

    def getItem(self, k):
        if k < 0 or k >= self.__size:
            raise Exception("Index Out of Bound")
            return self.__array[k]

    def __resize(self, cap):
        new_array = self.__createArray(cap)
        for i in range(0, self.__size):  # copy previous items
            new_array[i] = self.__array[i]
        self.__array = new_array
        self.__capacity = cap

    def __createArray(self, cap):  # create array of a specific type
        if self.__type == "i":
            return array.array("i", [0] * cap)
        elif self.__type == "u":
            return array.array("u", ["-"] * cap)
        elif self.__type == "f":
            return array.array("f", [0.0] * cap)
        elif self.__type == "d":
            return array.array("d", [0.0] * cap)
            raise Exception(
                "Invalid data type. Available data types are: i for int, u for character, f for float, and d for double."

arr = DynamicArray("i")  # dynamic array of type int
print("Array Items:")
for i in range(0, arr.length()):

print("Delete the last item:", arr.pop())
print("New length:", arr.length())


Array Items:
Delete the last item: 8
New length: 3

Back to: Data Structure > Data Structure - Arrays

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