Issue #49 circular linked list

pydatastructs/linear_data_structures/__init__.py

@@ -13,6 +13,8 @@
 
 from .linked_lists import (
     SinglyLinkedList,
-    DoublyLinkedList
+    DoublyLinkedList,
+    SinglyCircularLinkedList,
+    DoublyCircularLinkedList
 )
 __all__.extend(linked_lists.__all__)

pydatastructs/linear_data_structures/linked_lists.py

@@ -2,7 +2,9 @@
 
 __all__ = [
     'SinglyLinkedList',
-    'DoublyLinkedList'
+    'DoublyLinkedList',
+    'SinglyCircularLinkedList',
+    'DoublyCircularLinkedList'
 ]
 
 class LinkedList(object):
@@ -27,6 +29,8 @@ def __str__(self):
         while current_node is not None:
             elements.append(current_node.data)
             current_node = current_node.next
+            if current_node == self.head:
+                break
         return str(elements)
 
 class DoublyLinkedList(LinkedList):
@@ -508,3 +512,219 @@ def __getitem__(self, index):
             current_node = current_node.next
             counter += 1
         return current_node
+
+class SinglyCircularLinkedList(SinglyLinkedList):
+    """
+    Represents Singly Circular Linked List.
+
+    Parent Class
+    ============
+
+    SinglyLinkedList.
+
+    Examples
+    ========
+
+    >>> from pydatastructs import SinglyCircularLinkedList
+    >>> scll = SinglyCircularLinkedList()
+    >>> scll.append(6)
+    >>> scll[0].data
+    6
+    >>> scll.head.data
+    6
+    >>> scll.append(5)
+    >>> scll.append_left(2)
+    >>> print(scll)
+    [2, 6, 5]
+    >>> scll[0].data = 7.2
+    >>> scll.extract(1).data
+    6
+    >>> print(scll)
+    [7.2, 5]
+
+    References
+    ==========
+
+    .. [1] https://en.wikipedia.org/wiki/Linked_list#Circular_linked_list
+    .. [2] https://www.geeksforgeeks.org/circular-singly-linked-list-insertion/
+
+    """
+
+    def insert_after(self, prev_node, data):
+        """
+        Inserts a new node after the prev_node.
+
+        Parameters
+        ==========
+
+        prev_node: LinkedListNode
+            The node after which the
+            new node is to be inserted.
+
+        data
+            Any valid data to be stored in the node.
+        """
+        super(SinglyCircularLinkedList, self).insert_after(prev_node, data)
+        if prev_node.next.next == self.head:
+            self.tail = prev_node.next
+
+    def insert_at(self, index, data):
+        """
+        Inserts a new node at the input index.
+
+        Parameters
+        ==========
+
+        index: int
+            An integer satisfying python indexing properties.
+
+        data
+            Any valid data to be stored in the node.
+        """
+        super(SinglyCircularLinkedList, self).insert_at(index, data)
+        if self.size == 1:
+            self.head.next = self.head
+        new_node = self.__getitem__(index)
+        if index == 0:
+            self.tail.next = new_node
+        if new_node.next == self.head:
+            self.tail = new_node
+
+    def extract(self, index):
+        """
+        Extracts the node at the index of the list.
+
+        Parameters
+        ==========
+
+        index: int
+            An integer satisfying python indexing properties.
+
+        Returns
+        =======
+
+        current_node: LinkedListNode
+            The node at index i.
+        """
+        node = super(SinglyCircularLinkedList, self).extract(index)
+        if self.tail is None:
+            self.head = None
+        elif index == 0:
+            self.tail.next = self.head
+        return node
+
+class DoublyCircularLinkedList(DoublyLinkedList):
+    """
+    Represents Doubly Circular Linked List
+
+    Examples
+    ========
+
+    >>> from pydatastructs import DoublyCircularLinkedList
+    >>> dcll = DoublyCircularLinkedList()
+    >>> dcll.append(6)
+    >>> dcll[0].data
+    6
+    >>> dcll.head.data
+    6
+    >>> dcll.append(5)
+    >>> dcll.append_left(2)
+    >>> print(dcll)
+    [2, 6, 5]
+    >>> dcll[0].data = 7.2
+    >>> dcll.extract(1).data
+    6
+    >>> print(dcll)
+    [7.2, 5]
+
+    References
+    ==========
+
+    .. [1] https://en.wikipedia.org/wiki/Linked_list#Circular_linked_list
+    .. [2] https://www.geeksforgeeks.org/doubly-circular-linked-list-set-1-introduction-and-insertion/
+
+    """
+    def insert_after(self, prev_node, data):
+        """
+        Inserts a new node after the prev_node.
+
+        Parameters
+        ==========
+
+        prev_node: LinkedListNode
+            The node after which the
+            new node is to be inserted.
+
+        data
+            Any valid data to be stored in the node.
+        """
+        super(DoublyCircularLinkedList, self).insert_after(prev_node, data)
+        if prev_node.next.next == self.head:
+            self.tail = prev_node.next
+
+    def insert_before(self, next_node, data):
+        """
+        Inserts a new node before the next_node.
+
+        Parameters
+        ==========
+
+        next_node: LinkedListNode
+            The node before which the
+            new node is to be inserted.
+
+        data
+            Any valid data to be stored in the node.
+        """
+        super(DoublyCircularLinkedList, self).insert_before(next_node,data)
+        if next_node == self.head:
+            self.head = next_node.prev
+
+    def insert_at(self, index, data):
+        """
+        Inserts a new node at the input index.
+
+        Parameters
+        ==========
+
+        index: int
+            An integer satisfying python indexing properties.
+
+        data
+            Any valid data to be stored in the node.
+        """
+        super(DoublyCircularLinkedList, self).insert_at(index, data)
+        if self.size == 1:
+            self.head.next = self.head
+            self.head.prev = self.head
+        new_node = self.__getitem__(index)
+        if index == 0:
+            self.tail.next = new_node
+            new_node.prev = self.tail
+        if new_node.next == self.head:
+            self.tail = new_node
+            new_node.next = self.head
+            self.head.prev = new_node
+
+    def extract(self, index):
+        """
+        Extracts the node at the index of the list.
+
+        Parameters
+        ==========
+
+        index: int
+            An integer satisfying python indexing properties.
+
+        Returns
+        =======
+
+        current_node: LinkedListNode
+            The node at index i.
+        """
+        node = super(DoublyCircularLinkedList, self).extract(index)
+        if self.tail is None:
+            self.head = None
+        elif index == 0:
+            self.tail.next = self.head
+        return node

pydatastructs/linear_data_structures/tests/test_linked_lists.py

@@ -1,4 +1,4 @@
-from pydatastructs.linear_data_structures import DoublyLinkedList, SinglyLinkedList
+from pydatastructs.linear_data_structures import DoublyLinkedList, SinglyLinkedList, SinglyCircularLinkedList, DoublyCircularLinkedList
 from pydatastructs.utils.raises_util import raises
 import copy, random
 
@@ -69,3 +69,71 @@ def test_SinglyLinkedList():
         sll_copy.extract(index)
     assert str(sll_copy) == "[]"
     assert raises(ValueError, lambda: sll_copy.extract(1))
+
+def test_SinglyCircularLinkedList():
+    random.seed(1000)
+    scll = SinglyCircularLinkedList()
+    assert raises(IndexError, lambda: scll[2])
+    scll.append_left(5)
+    scll.append(1)
+    scll.append_left(2)
+    scll.append(3)
+    scll.insert_after(scll[1], 4)
+    scll.insert_after(scll[-1], 6)
+    scll.insert_at(0, 2)
+    scll.insert_at(-1, 9)
+    scll.extract(2)
+    scll.extract(0)
+    scll.extract(-1)
+    scll[-2].data = 0
+    assert str(scll) == "[2, 4, 1, 0, 9]"
+    assert len(scll) == 5
+    assert raises(IndexError, lambda: scll.insert_at(6, None))
+    assert raises(IndexError, lambda: scll.extract(20))
+    scll_copy = copy.deepcopy(scll)
+    for i in range(len(scll)):
+        if i%2 == 0:
+            scll.pop_left()
+        else:
+            scll.pop_right()
+    assert str(scll) == "[]"
+    for _ in range(len(scll_copy)):
+        index = random.randint(0, len(scll_copy) - 1)
+        scll_copy.extract(index)
+    assert str(scll_copy) == "[]"
+    assert raises(ValueError, lambda: scll_copy.extract(1))
+
+def test_DoublyCircularLinkedList():
+    random.seed(1000)
+    dcll = DoublyCircularLinkedList()
+    assert raises(IndexError, lambda: dcll[2])
+    dcll.append_left(5)
+    dcll.append(1)
+    dcll.append_left(2)
+    dcll.append(3)
+    dcll.insert_after(dcll[-1], 4)
+    dcll.insert_after(dcll[2], 6)
+    dcll.insert_before(dcll[4], 1)
+    dcll.insert_before(dcll[0], 7)
+    dcll.insert_at(0, 2)
+    dcll.insert_at(-1, 9)
+    dcll.extract(2)
+    dcll.extract(0)
+    dcll.extract(-1)
+    dcll[-2].data = 0
+    assert str(dcll) == "[7, 5, 1, 6, 1, 0, 9]"
+    assert len(dcll) == 7
+    assert raises(IndexError, lambda: dcll.insert_at(8, None))
+    assert raises(IndexError, lambda: dcll.extract(20))
+    dcll_copy = copy.deepcopy(dcll)
+    for i in range(len(dcll)):
+        if i%2 == 0:
+            dcll.pop_left()
+        else:
+            dcll.pop_right()
+    assert str(dcll) == "[]"
+    for _ in range(len(dcll_copy)):
+        index = random.randint(0, len(dcll_copy) - 1)
+        dcll_copy.extract(index)
+    assert str(dcll_copy) == "[]"
+    assert raises(ValueError, lambda: dcll_copy.extract(1))