Added postfix-prefix conversion

DIRECTORY.md

@@ -350,6 +350,7 @@
     * [Lexicographical Numbers](data_structures/stacks/lexicographical_numbers.py)
     * [Next Greater Element](data_structures/stacks/next_greater_element.py)
     * [Postfix Evaluation](data_structures/stacks/postfix_evaluation.py)
+    * [Postfix To Prefix Conversion](data_structures/stacks/postfix_to_prefix_conversion.py)
     * [Prefix Evaluation](data_structures/stacks/prefix_evaluation.py)
     * [Stack](data_structures/stacks/stack.py)
     * [Stack Using Two Queues](data_structures/stacks/stack_using_two_queues.py)
@@ -986,6 +987,7 @@
   * [Doppler Frequency](physics/doppler_frequency.py)
   * [Escape Velocity](physics/escape_velocity.py)
   * [Grahams Law](physics/grahams_law.py)
+  * [Hamiltonian](physics/hamiltonian.py)
   * [Horizontal Projectile Motion](physics/horizontal_projectile_motion.py)
   * [Hubble Parameter](physics/hubble_parameter.py)
   * [Ideal Gas Law](physics/ideal_gas_law.py)

data_structures/stacks/postfix_to_prefix_conversion.py

@@ -0,0 +1,49 @@
+"""
+Functions:
+- postfix_to_prefix(expression): Converts a postfix expression to a prefix expression.
+"""
+
+from .stack import Stack
+
+
+def postfix_to_prefix(expression_str: str) -> str:
+    """
+    Converts a postfix expression to a prefix expression.
+
+    Args:
+        expression (str): A string representing a postfix expression.
+
+    Returns:
+        str: A string representing the equivalent prefix expression.
+
+    Raises:
+        IndexError: If the expression is invalid or contains an invalid operator.
+
+    Example:
+        >>> postfix_to_prefix('23+5*')
+        '*+235'
+    """
+    stack: Stack[str] = Stack()
+    operators = {"+", "-", "*", "/", "^"}
+
+    for char in expression_str:
+        if char not in operators:
+            stack.push(char)
+        else:
+            operand1 = stack.pop()
+            operand2 = stack.pop()
+            stack.push(char + operand2 + operand1)
+
+    return stack.pop()
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()
+    postfix_expression = "ab+c*"
+
+    print("Postfix to infix demo\n")
+    print("Postfix expression:", postfix_expression)
+    prefix_expression = postfix_to_prefix(postfix_expression)
+    print("Prefix expression:", prefix_expression)