86. Partition List.

    - Language: Python.
    - Time complexity: O(n).
    - Space complexity: O(1).
    - Method: Swapping node using pointers (Dummy node).

Author: welder87

python_solutions/lc_86_partition_list/__init__.py

@@ -0,0 +1,22 @@
+from typing import Optional
+
+from common_datastructures import ListNode
+
+
+class Solution:
+    def partition(self, head: Optional[ListNode], x: int) -> Optional[ListNode]:
+        # Time complexity: O(n). Space complexity: O(1).
+        dummy_lt, dummy_ge = ListNode(val=-1000), ListNode(val=1000)
+        lt, ge = dummy_lt, dummy_ge
+        while head is not None:
+            spam = head.next
+            head.next = None
+            if head.val >= x:
+                ge.next = head
+                ge = ge.next
+            else:
+                lt.next = head
+                lt = lt.next
+            head = spam
+        lt.next = dummy_ge.next
+        return dummy_lt.next

python_solutions/lc_86_partition_list/lc_86_partition_list.py

@@ -0,0 +1,38 @@
+import pytest
+
+from common_datastructures import (
+    compare_singly_linked_lists,
+    to_list,
+    to_singly_linked_list,
+)
+from lc_86_partition_list.lc_86_partition_list import Solution
+
+test_cases = (
+    # preset cases
+    ([1, 4, 3, 2, 5, 2], 3, [1, 2, 2, 4, 3, 5]),
+    ([2, 1], 2, [1, 2]),
+    # common cases
+    ([4, 3, 5, -2, 0, -2], 3, [-2, 0, -2, 4, 3, 5]),
+    ([4, 3, 5, -2, 0, -2], 5, [4, 3, -2, 0, -2, 5]),
+    ([4, 3, 5, -2, 0, -2], 1, [-2, 0, -2, 4, 3, 5]),
+    ([4, 3, 5, -2, 0, -2], 0, [-2, -2, 4, 3, 5, 0]),
+    ([4, 3, 5, -2, 0, -2], -2, [4, 3, 5, -2, 0, -2]),
+    ([4, 3, 5, -2, 0, -2], 10, [4, 3, 5, -2, 0, -2]),
+    ([4, 3, 5, -2, 0, -2], -5, [4, 3, 5, -2, 0, -2]),
+    # corner cases
+    ([-1], 2, [-1]),
+    ([5], 2, [5]),
+    ([], 2, []),
+)
+
+
+@pytest.mark.parametrize(("lst", "x", "ans"), test_cases)
+def test_success_v0(lst: list[int], x: int, ans: list[int], solution: Solution):
+    res = solution.partition(to_singly_linked_list(lst), x)
+    assert to_list(res) == ans
+    assert compare_singly_linked_lists(res, to_singly_linked_list(ans))
+
+
+@pytest.fixture
+def solution() -> Solution:
+    return Solution()