Merge branch 'TheAlgorithms:master' into master

Author: kimtth

data_structures/linked_list/doubly_linked_list_two.py

@@ -9,25 +9,19 @@
      Delete operation is more efficient
 """
 
+from dataclasses import dataclass
+from typing import Self
 
+
+@dataclass
 class Node:
-    def __init__(self, data: int, previous=None, next_node=None):
-        self.data = data
-        self.previous = previous
-        self.next = next_node
+    data: int
+    previous: Self | None = None
+    next: Self | None = None
 
     def __str__(self) -> str:
         return f"{self.data}"
 
-    def get_data(self) -> int:
-        return self.data
-
-    def get_next(self):
-        return self.next
-
-    def get_previous(self):
-        return self.previous
-
 
 class LinkedListIterator:
     def __init__(self, head):
@@ -40,43 +34,43 @@ def __next__(self):
         if not self.current:
             raise StopIteration
         else:
-            value = self.current.get_data()
-            self.current = self.current.get_next()
+            value = self.current.data
+            self.current = self.current.next
             return value
 
 
+@dataclass
 class LinkedList:
-    def __init__(self):
-        self.head = None  # First node in list
-        self.tail = None  # Last node in list
+    head: Node | None = None  # First node in list
+    tail: Node | None = None  # Last node in list
 
     def __str__(self):
         current = self.head
         nodes = []
         while current is not None:
-            nodes.append(current.get_data())
-            current = current.get_next()
+            nodes.append(current.data)
+            current = current.next
         return " ".join(str(node) for node in nodes)
 
     def __contains__(self, value: int):
         current = self.head
         while current:
-            if current.get_data() == value:
+            if current.data == value:
                 return True
-            current = current.get_next()
+            current = current.next
         return False
 
     def __iter__(self):
         return LinkedListIterator(self.head)
 
     def get_head_data(self):
         if self.head:
-            return self.head.get_data()
+            return self.head.data
         return None
 
     def get_tail_data(self):
         if self.tail:
-            return self.tail.get_data()
+            return self.tail.data
         return None
 
     def set_head(self, node: Node) -> None:
@@ -87,8 +81,9 @@ def set_head(self, node: Node) -> None:
             self.insert_before_node(self.head, node)
 
     def set_tail(self, node: Node) -> None:
-        if self.head is None:
-            self.set_head(node)
+        if self.tail is None:
+            self.head = node
+            self.tail = node
         else:
             self.insert_after_node(self.tail, node)
 
@@ -103,7 +98,7 @@ def insert_before_node(self, node: Node, node_to_insert: Node) -> None:
         node_to_insert.next = node
         node_to_insert.previous = node.previous
 
-        if node.get_previous() is None:
+        if node.previous is None:
             self.head = node_to_insert
         else:
             node.previous.next = node_to_insert
@@ -114,7 +109,7 @@ def insert_after_node(self, node: Node, node_to_insert: Node) -> None:
         node_to_insert.previous = node
         node_to_insert.next = node.next
 
-        if node.get_next() is None:
+        if node.next is None:
             self.tail = node_to_insert
         else:
             node.next.previous = node_to_insert
@@ -131,32 +126,32 @@ def insert_at_position(self, position: int, value: int) -> None:
                 return
             current_position += 1
             node = node.next
-        self.insert_after_node(self.tail, new_node)
+        self.set_tail(new_node)
 
     def get_node(self, item: int) -> Node:
         node = self.head
         while node:
-            if node.get_data() == item:
+            if node.data == item:
                 return node
-            node = node.get_next()
+            node = node.next
         raise Exception("Node not found")
 
     def delete_value(self, value):
         if (node := self.get_node(value)) is not None:
             if node == self.head:
-                self.head = self.head.get_next()
+                self.head = self.head.next
 
             if node == self.tail:
-                self.tail = self.tail.get_previous()
+                self.tail = self.tail.previous
 
             self.remove_node_pointers(node)
 
     @staticmethod
     def remove_node_pointers(node: Node) -> None:
-        if node.get_next():
+        if node.next:
             node.next.previous = node.previous
 
-        if node.get_previous():
+        if node.previous:
             node.previous.next = node.next
 
         node.next = None
@@ -241,6 +236,22 @@ def create_linked_list() -> None:
     7
     8
     9
+    >>> linked_list = LinkedList()
+    >>> linked_list.insert_at_position(position=1, value=10)
+    >>> str(linked_list)
+    '10'
+    >>> linked_list.insert_at_position(position=2, value=20)
+    >>> str(linked_list)
+    '10 20'
+    >>> linked_list.insert_at_position(position=1, value=30)
+    >>> str(linked_list)
+    '30 10 20'
+    >>> linked_list.insert_at_position(position=3, value=40)
+    >>> str(linked_list)
+    '30 10 40 20'
+    >>> linked_list.insert_at_position(position=5, value=50)
+    >>> str(linked_list)
+    '30 10 40 20 50'
     """
 
 

data_structures/stacks/prefix_evaluation.py

@@ -1,8 +1,9 @@
 """
-Python3 program to evaluate a prefix expression.
+Program to evaluate a prefix expression.
+https://en.wikipedia.org/wiki/Polish_notation
 """
 
-calc = {
+operators = {
     "+": lambda x, y: x + y,
     "-": lambda x, y: x - y,
     "*": lambda x, y: x * y,
@@ -31,6 +32,10 @@ def evaluate(expression):
     21
     >>> evaluate("/ * 10 2 + 4 1 ")
     4.0
+    >>> evaluate("2")
+    2
+    >>> evaluate("+ * 2 3 / 8 4")
+    8.0
     """
     stack = []
 
@@ -45,11 +50,39 @@ def evaluate(expression):
             # push the result onto the stack again
             o1 = stack.pop()
             o2 = stack.pop()
-            stack.append(calc[c](o1, o2))
+            stack.append(operators[c](o1, o2))
 
     return stack.pop()
 
 
+def evaluate_recursive(expression: list[str]):
+    """
+    Alternative recursive implementation
+
+    >>> evaluate_recursive(['2'])
+    2
+    >>> expression = ['+', '*', '2', '3', '/', '8', '4']
+    >>> evaluate_recursive(expression)
+    8.0
+    >>> expression
+    []
+    >>> evaluate_recursive(['+', '9', '*', '2', '6'])
+    21
+    >>> evaluate_recursive(['/', '*', '10', '2', '+', '4', '1'])
+    4.0
+    """
+
+    op = expression.pop(0)
+    if is_operand(op):
+        return int(op)
+
+    operation = operators[op]
+
+    a = evaluate_recursive(expression)
+    b = evaluate_recursive(expression)
+    return operation(a, b)
+
+
 # Driver code
 if __name__ == "__main__":
     test_expression = "+ 9 * 2 6"