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Added utility for doubly-linked lists
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‎2020/doubly_linked_list.py

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class DoublyLinkedList:
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def __init__(self, is_cycle=False):
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"""
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Creates a list
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:param Boolean is_cycle: Whether the list is a cycle (loops around itself)
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"""
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self.start_element = None
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self.is_cycle = is_cycle
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self.elements = {}
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def insert(self, ref_element, new_elements, insert_before=False):
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"""
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Inserts new elements in the list
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:param Any ref_element: The value of the element where we'll insert data
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:param Any new_elements: A list of new elements to insert, or a single element
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:param Boolean insert_before: If True, will insert before ref_element.
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"""
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new_elements_converted = []
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if isinstance(new_elements, (list, tuple, set)):
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for i, element in enumerate(new_elements):
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if not isinstance(element, DoublyLinkedListElement):
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new_element_converted = DoublyLinkedListElement(element)
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if i != 0:
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new_element_converted.prev_element = new_elements_converted[
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i - 1
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]
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new_element_converted.prev_element.next_element = (
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new_element_converted
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)
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else:
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new_element_converted = element
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if i != 0:
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new_element_converted.prev_element = new_elements_converted[
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i - 1
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]
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new_element_converted.prev_element.next_element = (
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new_element_converted
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)
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new_elements_converted.append(new_element_converted)
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self.elements[new_element_converted.item] = new_element_converted
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else:
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if not isinstance(new_elements, DoublyLinkedListElement):
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new_element_converted = DoublyLinkedListElement(new_elements)
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else:
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new_element_converted = new_elements
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new_elements_converted.append(new_element_converted)
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self.elements[new_element_converted.item] = new_element_converted
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if self.start_element == None:
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self.start_element = new_elements_converted[0]
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for pos, element in enumerate(new_elements_converted):
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element.prev_element = new_elements_converted[pos - 1]
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element.next_element = new_elements_converted[pos + 1]
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if not self.is_cycle:
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new_elements_converted[0].prev_element = None
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new_elements_converted[-1].next_element = None
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else:
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if isinstance(ref_element, DoublyLinkedListElement):
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cursor = ref_element
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else:
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cursor = self.find(ref_element)
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if insert_before:
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new_elements_converted[0].prev_element = cursor.prev_element
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new_elements_converted[-1].next_element = cursor
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if cursor.prev_element is not None:
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cursor.prev_element.next_element = new_elements_converted[0]
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cursor.prev_element = new_elements_converted[-1]
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if self.start_element == cursor:
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self.start_element = new_elements_converted[0]
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else:
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new_elements_converted[0].prev_element = cursor
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new_elements_converted[-1].next_element = cursor.next_element
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if cursor.next_element is not None:
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cursor.next_element.prev_element = new_elements_converted[-1]
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cursor.next_element = new_elements_converted[0]
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def append(self, new_element):
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"""
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Appends an element in the list
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:param Any new_element: The new element to insert
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:param Boolean insert_before: If True, will insert before ref_element.
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"""
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if not isinstance(new_element, DoublyLinkedListElement):
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new_element = DoublyLinkedListElement(new_element)
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self.elements[new_element.item] = new_element
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if self.start_element is None:
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self.start_element = new_element
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if self.is_cycle:
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new_element.next_element = new_element
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new_element.prev_element = new_element
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else:
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if self.is_cycle:
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cursor = self.start_element.prev_element
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else:
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cursor = self.start_element
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while cursor.next_element is not None:
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if self.is_cycle and cursor.next_element == self.start_element:
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break
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cursor = cursor.next_element
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new_element.prev_element = cursor
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new_element.next_element = cursor.next_element
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if cursor.next_element is not None:
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cursor.next_element.prev_element = new_element
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cursor.next_element = new_element
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def traverse(self, start, end=None):
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"""
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Gets items based on their values
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:param Any start: The start element
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:param Any stop: The end element
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"""
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output = []
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if self.start_element is None:
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return []
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if not isinstance(start, DoublyLinkedListElement):
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start = self.find(start)
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cursor = start
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if not isinstance(end, DoublyLinkedListElement):
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end = self.find(end)
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while cursor is not None:
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if cursor == end:
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break
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output.append(cursor)
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cursor = cursor.next_element
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if self.is_cycle and cursor == start:
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break
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return output
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def delete_by_value(self, to_delete):
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"""
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Deletes a given element from the list
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:param Any to_delete: The element to delete
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"""
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output = []
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if self.start_element is None:
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return
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cursor = to_delete
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cursor.prev_element.next_element = cursor.next_element
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cursor.next_element.prev_element = cursor.prev_element
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def delete_by_position(self, to_delete):
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"""
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Deletes a given element from the list
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:param Any to_delete: The element to delete
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"""
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output = []
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if self.start_element is None:
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return
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if not isinstance(to_delete, int):
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raise TypeError("Position must be an integer")
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cursor = self.start_element
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i = -1
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while cursor is not None and i < to_delete:
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i += 1
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if i == to_delete:
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if cursor.prev_element:
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cursor.prev_element.next_element = cursor.next_element
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if cursor.next_element:
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cursor.next_element.prev_element = cursor.prev_element
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if self.start_element == cursor:
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self.start_element = cursor.next_element
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del cursor
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return True
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raise ValueError("Element not in list")
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def find(self, needle):
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"""
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Finds a given item based on its value
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:param Any needle: The element to search
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"""
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if isinstance(needle, DoublyLinkedListElement):
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return needle
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else:
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if needle in self.elements:
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return self.elements[needle]
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else:
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return False
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class DoublyLinkedListElement:
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def __init__(self, data, prev_element=None, next_element=None):
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self.item = data
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self.prev_element = prev_element
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self.next_element = next_element
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def __repr__(self):
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output = [self.item]
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if self.prev_element is not None:
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output.append(self.prev_element.item)
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else:
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output.append(None)
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if self.next_element is not None:
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output.append(self.next_element.item)
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else:
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output.append(None)
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return str(tuple(output))

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