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| 1 | +# Singly Linked List (a.k.a Linked List) Implementation |
| 2 | + |
| 3 | +class Node: |
| 4 | + """Node implementation. |
| 5 | + """ |
| 6 | + |
| 7 | + def __init__(self, value) -> None: |
| 8 | + """Class constructor. |
| 9 | +
|
| 10 | + Args: |
| 11 | + value (_type_): Value associated with each node. |
| 12 | + """ |
| 13 | + self.value = value |
| 14 | + self.next = None |
| 15 | + |
| 16 | + |
| 17 | +class SinglyLinkedList: |
| 18 | + """Singly linked list implementation. |
| 19 | + """ |
| 20 | + |
| 21 | + def __init__(self) -> None: |
| 22 | + """Class constructor. |
| 23 | + """ |
| 24 | + self.head = None |
| 25 | + |
| 26 | + def insert_at_head(self, value) -> None: |
| 27 | + """Method to insert node at the head of the linked list. |
| 28 | +
|
| 29 | + Args: |
| 30 | + value (_type_): Value to be inserted at the head of the linked list. |
| 31 | + """ |
| 32 | + if self.head is None: |
| 33 | + self.head = new_node |
| 34 | + return |
| 35 | + |
| 36 | + new_node = Node(value=value) |
| 37 | + new_node.next = self.head |
| 38 | + self.head = new_node |
| 39 | + |
| 40 | + def insert_at_tail(self, value) -> None: |
| 41 | + """Method to insert node at the tail of the linked list. |
| 42 | +
|
| 43 | + Args: |
| 44 | + value (_type_): Value to be inserted at the tail of the linked list. |
| 45 | + """ |
| 46 | + if self.head is None: |
| 47 | + self.insert_at_head(value=value) |
| 48 | + return |
| 49 | + |
| 50 | + curr = self.head |
| 51 | + while curr.next is not None: |
| 52 | + curr = curr.next |
| 53 | + |
| 54 | + curr.next = Node(value=value) |
| 55 | + |
| 56 | + def insert_at_position(self, value, position) -> None: |
| 57 | + """Method to insert aa node with associated value at a `position`. |
| 58 | +
|
| 59 | + Args: |
| 60 | + value (_type_): Value to be inserted in the linked list. |
| 61 | + position (_type_): Position (positive integer) at which a value is to be inserted. |
| 62 | +
|
| 63 | + Raises: |
| 64 | + ValueError: If `position` is greater than the actual size of the linked list. |
| 65 | + """ |
| 66 | + assert position >= 0 |
| 67 | + |
| 68 | + if self.get_size() < position: |
| 69 | + raise ValueError("Invalid position.") |
| 70 | + |
| 71 | + if position == 0: |
| 72 | + self.insert_at_head(value=value) |
| 73 | + return |
| 74 | + |
| 75 | + curr = self.head |
| 76 | + count = 0 |
| 77 | + while count != position-1: |
| 78 | + curr = curr.next |
| 79 | + count += 1 |
| 80 | + |
| 81 | + new_node = Node(value) |
| 82 | + new_node.next = curr.next |
| 83 | + curr.next = new_node |
| 84 | + |
| 85 | + def delete_at_position(self, position: int) -> None: |
| 86 | + """Method to delete value at `position` from the linked list. |
| 87 | +
|
| 88 | + Args: |
| 89 | + position (int): Position (postive integer) for which value has to be deleted. |
| 90 | +
|
| 91 | + Raises: |
| 92 | + ValueError: If `position` is greater than the actual size of the linked list or empty linked list. |
| 93 | + """ |
| 94 | + assert position >= 0 |
| 95 | + |
| 96 | + if self.get_size() < position or self.is_empty(): |
| 97 | + raise ValueError("Invalid position. Cannot delete.") |
| 98 | + |
| 99 | + if position == 0: |
| 100 | + self.head = self.head.next |
| 101 | + return |
| 102 | + |
| 103 | + count = 0 |
| 104 | + curr = self.head |
| 105 | + while count != position-1: |
| 106 | + curr = curr.next |
| 107 | + count += 1 |
| 108 | + |
| 109 | + curr.next = curr.next.next |
| 110 | + |
| 111 | + def reverse(self) -> None: |
| 112 | + """Method to reverse the linked list. |
| 113 | + """ |
| 114 | + if self.is_empty(): |
| 115 | + return 0 |
| 116 | + |
| 117 | + prev = None |
| 118 | + curr = self.head |
| 119 | + |
| 120 | + while curr is not None: |
| 121 | + next_node = curr.next |
| 122 | + curr.next = prev |
| 123 | + prev = curr |
| 124 | + curr = next_node |
| 125 | + |
| 126 | + self.head = prev |
| 127 | + |
| 128 | + def is_empty(self) -> bool: |
| 129 | + """Method to check if the linked list is empty. |
| 130 | +
|
| 131 | + Returns: |
| 132 | + bool: Returns a boolean `True` if empty, `False` otherwise. |
| 133 | + """ |
| 134 | + if self.head is None: |
| 135 | + return True |
| 136 | + |
| 137 | + return False |
| 138 | + |
| 139 | + def get_size(self) -> int: |
| 140 | + """Method to count the number of nodes in the linked list/ |
| 141 | +
|
| 142 | + Returns: |
| 143 | + int: Returns the count of number of nodes. |
| 144 | + """ |
| 145 | + if self.is_empty(): |
| 146 | + return 0 |
| 147 | + |
| 148 | + count = 0 |
| 149 | + curr = self.head |
| 150 | + while curr is not None: |
| 151 | + count += 1 |
| 152 | + curr = curr.next |
| 153 | + |
| 154 | + return count |
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