print reverse: A LinkedList with a tail pointer (#9875)

* print reverse: A LinkedList with a tail pointer

* updating DIRECTORY.md

---------

Co-authored-by: github-actions <${GITHUB_ACTOR}@users.noreply.github.com>

DIRECTORY.md

@@ -50,6 +50,7 @@
   * [Index Of Rightmost Set Bit](bit_manipulation/index_of_rightmost_set_bit.py)
   * [Is Even](bit_manipulation/is_even.py)
   * [Is Power Of Two](bit_manipulation/is_power_of_two.py)
+  * [Largest Pow Of Two Le Num](bit_manipulation/largest_pow_of_two_le_num.py)
   * [Missing Number](bit_manipulation/missing_number.py)
   * [Numbers Different Signs](bit_manipulation/numbers_different_signs.py)
   * [Reverse Bits](bit_manipulation/reverse_bits.py)
@@ -322,6 +323,7 @@
   * [Integer Partition](dynamic_programming/integer_partition.py)
   * [Iterating Through Submasks](dynamic_programming/iterating_through_submasks.py)
   * [Knapsack](dynamic_programming/knapsack.py)
+  * [Largest Divisible Subset](dynamic_programming/largest_divisible_subset.py)
   * [Longest Common Subsequence](dynamic_programming/longest_common_subsequence.py)
   * [Longest Common Substring](dynamic_programming/longest_common_substring.py)
   * [Longest Increasing Subsequence](dynamic_programming/longest_increasing_subsequence.py)
@@ -460,6 +462,7 @@
 ## Greedy Methods
   * [Fractional Knapsack](greedy_methods/fractional_knapsack.py)
   * [Fractional Knapsack 2](greedy_methods/fractional_knapsack_2.py)
+  * [Gas Station](greedy_methods/gas_station.py)
   * [Minimum Waiting Time](greedy_methods/minimum_waiting_time.py)
   * [Optimal Merge Pattern](greedy_methods/optimal_merge_pattern.py)
 
@@ -542,6 +545,7 @@
   * [Average Median](maths/average_median.py)
   * [Average Mode](maths/average_mode.py)
   * [Bailey Borwein Plouffe](maths/bailey_borwein_plouffe.py)
+  * [Base Neg2 Conversion](maths/base_neg2_conversion.py)
   * [Basic Maths](maths/basic_maths.py)
   * [Bell Numbers](maths/bell_numbers.py)
   * [Binary Exp Mod](maths/binary_exp_mod.py)
@@ -657,7 +661,6 @@
     * [P Series](maths/series/p_series.py)
   * [Sieve Of Eratosthenes](maths/sieve_of_eratosthenes.py)
   * [Sigmoid](maths/sigmoid.py)
-  * [Sigmoid Linear Unit](maths/sigmoid_linear_unit.py)
   * [Signum](maths/signum.py)
   * [Simpson Rule](maths/simpson_rule.py)
   * [Simultaneous Linear Equation Solver](maths/simultaneous_linear_equation_solver.py)
@@ -716,6 +719,7 @@
     * [Leaky Rectified Linear Unit](neural_network/activation_functions/leaky_rectified_linear_unit.py)
     * [Rectified Linear Unit](neural_network/activation_functions/rectified_linear_unit.py)
     * [Scaled Exponential Linear Unit](neural_network/activation_functions/scaled_exponential_linear_unit.py)
+    * [Sigmoid Linear Unit](neural_network/activation_functions/sigmoid_linear_unit.py)
   * [Back Propagation Neural Network](neural_network/back_propagation_neural_network.py)
   * [Convolution Neural Network](neural_network/convolution_neural_network.py)
   * [Perceptron](neural_network/perceptron.py)
@@ -1180,6 +1184,7 @@
   * [Naive String Search](strings/naive_string_search.py)
   * [Ngram](strings/ngram.py)
   * [Palindrome](strings/palindrome.py)
+  * [Pig Latin](strings/pig_latin.py)
   * [Prefix Function](strings/prefix_function.py)
   * [Rabin Karp](strings/rabin_karp.py)
   * [Remove Duplicate](strings/remove_duplicate.py)

data_structures/linked_list/print_reverse.py

@@ -1,22 +1,91 @@
 from __future__ import annotations
 
+from collections.abc import Iterable, Iterator
+from dataclasses import dataclass
 
+
+@dataclass
 class Node:
-    def __init__(self, data=None):
-        self.data = data
-        self.next = None
-
-    def __repr__(self):
-        """Returns a visual representation of the node and all its following nodes."""
-        string_rep = []
-        temp = self
-        while temp:
-            string_rep.append(f"{temp.data}")
-            temp = temp.next
-        return "->".join(string_rep)
+    data: int
+    next_node: Node | None = None
 
 
-def make_linked_list(elements_list: list):
+class LinkedList:
+    """A class to represent a Linked List.
+    Use a tail pointer to speed up the append() operation.
+    """
+
+    def __init__(self) -> None:
+        """Initialize a LinkedList with the head node set to None.
+        >>> linked_list = LinkedList()
+        >>> (linked_list.head, linked_list.tail)
+        (None, None)
+        """
+        self.head: Node | None = None
+        self.tail: Node | None = None  # Speeds up the append() operation
+
+    def __iter__(self) -> Iterator[int]:
+        """Iterate the LinkedList yielding each Node's data.
+        >>> linked_list = LinkedList()
+        >>> items = (1, 2, 3, 4, 5)
+        >>> linked_list.extend(items)
+        >>> tuple(linked_list) == items
+        True
+        """
+        node = self.head
+        while node:
+            yield node.data
+            node = node.next_node
+
+    def __repr__(self) -> str:
+        """Returns a string representation of the LinkedList.
+        >>> linked_list = LinkedList()
+        >>> str(linked_list)
+        ''
+        >>> linked_list.append(1)
+        >>> str(linked_list)
+        '1'
+        >>> linked_list.extend([2, 3, 4, 5])
+        >>> str(linked_list)
+        '1 -> 2 -> 3 -> 4 -> 5'
+        """
+        return " -> ".join([str(data) for data in self])
+
+    def append(self, data: int) -> None:
+        """Appends a new node with the given data to the end of the LinkedList.
+        >>> linked_list = LinkedList()
+        >>> str(linked_list)
+        ''
+        >>> linked_list.append(1)
+        >>> str(linked_list)
+        '1'
+        >>> linked_list.append(2)
+        >>> str(linked_list)
+        '1 -> 2'
+        """
+        if self.tail:
+            self.tail.next_node = self.tail = Node(data)
+        else:
+            self.head = self.tail = Node(data)
+
+    def extend(self, items: Iterable[int]) -> None:
+        """Appends each item to the end of the LinkedList.
+        >>> linked_list = LinkedList()
+        >>> linked_list.extend([])
+        >>> str(linked_list)
+        ''
+        >>> linked_list.extend([1, 2])
+        >>> str(linked_list)
+        '1 -> 2'
+        >>> linked_list.extend([3,4])
+        >>> str(linked_list)
+        '1 -> 2 -> 3 -> 4'
+        """
+        for item in items:
+            self.append(item)
+
+
+def make_linked_list(elements_list: Iterable[int]) -> LinkedList:
     """Creates a Linked List from the elements of the given sequence
     (list/tuple) and returns the head of the Linked List.
     >>> make_linked_list([])
@@ -28,43 +97,30 @@ def make_linked_list(elements_list: list):
     >>> make_linked_list(['abc'])
     abc
     >>> make_linked_list([7, 25])
-    7->25
+    7 -> 25
     """
     if not elements_list:
         raise Exception("The Elements List is empty")
 
-    current = head = Node(elements_list[0])
-    for i in range(1, len(elements_list)):
-        current.next = Node(elements_list[i])
-        current = current.next
-    return head
+    linked_list = LinkedList()
+    linked_list.extend(elements_list)
+    return linked_list
 
 
-def print_reverse(head_node: Node) -> None:
+def in_reverse(linked_list: LinkedList) -> str:
     """Prints the elements of the given Linked List in reverse order
-    >>> print_reverse([])
-    >>> linked_list = make_linked_list([69, 88, 73])
-    >>> print_reverse(linked_list)
-    73
-    88
-    69
+    >>> in_reverse(LinkedList())
+    ''
+    >>> in_reverse(make_linked_list([69, 88, 73]))
+    '73 <- 88 <- 69'
     """
-    if head_node is not None and isinstance(head_node, Node):
-        print_reverse(head_node.next)
-        print(head_node.data)
-
-
-def main():
-    from doctest import testmod
-
-    testmod()
-
-    linked_list = make_linked_list([14, 52, 14, 12, 43])
-    print("Linked List:")
-    print(linked_list)
-    print("Elements in Reverse:")
-    print_reverse(linked_list)
+    return " <- ".join(str(line) for line in reversed(tuple(linked_list)))
 
 
 if __name__ == "__main__":
-    main()
+    from doctest import testmod
+
+    testmod()
+    linked_list = make_linked_list((14, 52, 14, 12, 43))
+    print(f"Linked List:  {linked_list}")
+    print(f"Reverse List: {in_reverse(linked_list)}")