[pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

Author: pre-commit-ci[bot]

data_structures/arrays/sudoku_solver.py

@@ -25,6 +25,7 @@ def cross(items_a, items_b):
 units = {s: [u for u in unitlist if s in u] for s in squares}
 peers = {s: {x for u in units[s] for x in u} - {s} for s in squares}
 
+
 def test():
     "A set of unit tests."
     assert len(squares) == 81