README.md

Data Structures in Python

Neatly written data structures in Python! With Tests! Feel feel to use this as-is, or as a base for your own implementation!

Linked Lists

The first data structure in this series is Linked Lists!

Linked Lists still back some of the most powerful db solutions where write-speeds are important, they offer some significant advantages over other linear data structures. Unlike arrays, they are a dynamic data structure, resizable at run-time. Also, the insertion and deletion operations are efficient and easily implemented.

Example Usage

import unittest
from linked_list.SinglyLinkedList import *


class TestLinkedList(unittest.TestCase):

    def setUp(self) -> None:
        self.normal_list = list(range(10))
        self.linked_list = LinkedList(range(10))

    def _test_normal_list_and_linked_list(self):
        self.assertEqual(self.normal_list, self.linked_list.get_list())

    def test_get_list(self):
        self.assertEqual(self.linked_list.get_list(),
                         [node.val for node in self.linked_list])

    def test_append(self):
        self.normal_list.append(5)
        self.linked_list.append(5)
        self._test_normal_list_and_linked_list()

    def test_insert(self):
        start, mid, end = 0, len(self.normal_list) // 2, -1

        for i in start, mid, end:
            self.normal_list.insert(i, i)
            self.linked_list.insert(index=i, value=i)
            self._test_normal_list_and_linked_list()

        self.linked_list.insert(index=len(self.linked_list), value=1)
        self.normal_list.insert(len(self.normal_list), 1)
        self._test_normal_list_and_linked_list()

        # Index Error positive and negative
        try:
            self.linked_list.insert(index=len(self.linked_list) + 2, value=3)
            return False
        except IndexError:
            try:
                self.linked_list.insert(index=-(len(self.linked_list) + 2),
                                        value=3)
                return False
            except IndexError:
                return True

    def test_pop(self):
        start, mid, end = 0, len(self.normal_list) // 2, -1
        for i in start, mid, end:
            self.normal_list.pop(i)
            self.linked_list.pop(i)
            self._test_normal_list_and_linked_list()

    def test_pop_empty(self):
        new_ll = LinkedList()
        try:
            new_ll.pop()
        except UnderFlow:
            pass

    def test_remove(self):
        start, mid, end = 0, len(self.normal_list) // 2, -1
        for i in start, mid, end:
            self.normal_list.remove(self.normal_list[i])
            self.linked_list.remove(self.linked_list[i].val)
            self._test_normal_list_and_linked_list()

    def test_remove_element_not_present(self):
        new_ll = LinkedList([5, 10])
        try:
            new_ll.remove(15)
        except ElementNotFoundError:
            pass

    def test_reversal(self):
        self.assertEqual(list(reversed(self.normal_list)),
                         [node.val for node in reversed(self.linked_list)])

    def test_index_of(self):
        self.assertEqual(self.normal_list.index(self.normal_list[0]),
                         self.linked_list.index_of(self.linked_list.get(0)))

    def test_size(self):
        self.assertEqual(sum([1 for _ in self.linked_list]),
                         len(self.linked_list))

    def test_str(self):
        empty_ll = LinkedList()
        self.assertEqual(str(empty_ll), "[]")

        del empty_ll
        non_empty_ll = LinkedList(range(10))
        self.assertEqual(str(non_empty_ll), str(list(range(10))))

    def test_index_error(self):
        try:
            empty_ll = LinkedList()
            empty_ll[4]
            return False
        except IndexError:
            pass

    def test_set_item(self):
        try:
            self.linked_list[0] = 44
            return self.linked_list[0].val == 44
        except:
            return False

    def test_set(self):
        try:
            self.linked_list.set(index=0, value=11)
            return self.linked_list[0].val == 11
        except:
            return False

    def test_equality(self):
        list1 = LinkedList(range(10))
        list2 = LinkedList(range(10))
        self.assertEqual(list1, list2)
        self.assertNotEqual(list1, LinkedList())

    def test_sorted(self):
        ll = LinkedList([5, 4, 3, 2, 1])
        nl = [5, 4, 3, 2, 1]

        for ll_node, nl_val in zip(sorted(ll), sorted(nl)):
            self.assertEqual(ll_node.val, nl_val)

    def test_repr_head(self):
        ll = LinkedList([5])
        self.assertEqual(repr(ll[0]), "Node(5)")

    def test_add(self):
        ll = LinkedList(range(5))
        ll2 = LinkedList(range(5, 10))

        ll + ll2
        self.assertEqual(ll.get_list(), list(range(10)))

        ll = LinkedList()
        ll + ll2
        self.assertEqual(ll.get_list(), list(range(5, 10)))

        self.assertEqual(ll.get_list(), list(range(5, 10)))


if __name__ == '__main__':
    unittest.main(verbosity=2)

License

MIT