docs: Add detailed docstrings explaining Strassen algorithm complexity

- Added comprehensive docstring to strassen() function explaining:
  - Time complexity: O(n^2.807) vs O(n³) for standard multiplication
  - Space complexity: O(n²)
  - The 7 matrix multiplication formulas used
  - When the algorithm is beneficial (large matrices)
  - Input requirements (dimensions must be power of 2)

- Improved docstring for actual_strassen() with args and raises documentation

- Addresses issue #14084: adding better docstring explaining Strassen's complexity

Author: hiSandog

divide_and_conquer/strassen_matrix_multiplication.py

@@ -73,8 +73,28 @@ def print_matrix(matrix: list) -> None:
 
 def actual_strassen(matrix_a: list, matrix_b: list) -> list:
     """
-    Recursive function to calculate the product of two matrices, using the Strassen
-    Algorithm. It only supports square matrices of any size that is a power of 2.
+    Recursive function to calculate the product of two matrices using the Strassen
+    Algorithm.
+
+    This is the core recursive implementation that only supports square matrices
+    of size that is a power of 2 (e.g., 2x2, 4x4, 8x8, 16x16, etc.).
+
+    The algorithm works by:
+    1. Base case: For 2x2 matrices, use standard multiplication
+    2. Recursive case:
+       - Split both matrices into 4 quadrants
+       - Compute 7 products using the formulas above
+       - Combine the 7 products to get the final result
+
+    Args:
+        matrix_a: Square matrix with dimensions as power of 2
+        matrix_b: Square matrix with dimensions as power of 2
+
+    Returns:
+        Product matrix
+
+    Raises:
+        Exception: If matrices are not square or dimensions are not power of 2
     """
     if matrix_dimensions(matrix_a) == (2, 2):
         return default_matrix_multiplication(matrix_a, matrix_b)
@@ -106,6 +126,42 @@ def actual_strassen(matrix_a: list, matrix_b: list) -> list:
 
 def strassen(matrix1: list, matrix2: list) -> list:
     """
+    Multiplies two matrices using the Strassen algorithm for improved time complexity.
+
+    The Strassen algorithm reduces the complexity of matrix multiplication from
+    O(n³) to O(n^2.807) by reducing the number of recursive matrix multiplications
+    from 8 to 7. While the asymptotic complexity is better, the actual performance
+    improvement is typically seen only for large matrices due to higher constant
+    factors and additional overhead.
+
+    Time Complexity: O(n^2.807) - Strassen vs O(n³) for standard multiplication
+    Space Complexity: O(n²) for storing the result matrix
+
+    The algorithm works by recursively dividing matrices into 2x2 submatrices and
+    computing 7 products (P1-P7) instead of 8:
+        P1 = A * (F - H)
+        P2 = (A + B) * H
+        P3 = (C + D) * E
+        P4 = D * (G - E)
+        P5 = (A + D) * (E + H)
+        P6 = (B - D) * (G + H)
+        P7 = (A - C) * (E + F)
+
+    Then combines these products to get the final result matrix.
+
+    Note: This implementation requires input matrices to have dimensions that are
+    powers of 2. The function automatically pads matrices with zeros if needed.
+
+    Args:
+        matrix1: First matrix (m x n)
+        matrix2: Second matrix (n x p)
+
+    Returns:
+        Result matrix (m x p)
+
+    Raises:
+        Exception: If matrix dimensions are incompatible for multiplication
+
     >>> strassen([[2,1,3],[3,4,6],[1,4,2],[7,6,7]], [[4,2,3,4],[2,1,1,1],[8,6,4,2]])
     [[34, 23, 19, 15], [68, 46, 37, 28], [28, 18, 15, 12], [96, 62, 55, 48]]
     >>> strassen([[3,7,5,6,9],[1,5,3,7,8],[1,4,4,5,7]], [[2,4],[5,2],[1,7],[5,5],[7,8]])