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

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Author: pre-commit-ci[bot]

data_structures/disjoint_set/disjoint_set.py

@@ -2,8 +2,10 @@
 Disjoint set.
 Reference: https://en.wikipedia.org/wiki/Disjoint-set_data_structure
 """
+
 from dataclasses import dataclass
 
+
 @dataclass
 class Node:
     data: int