"Find Mode in Binary Search Tree" solution

src/find_mode_in_binary_search_tree.py

@@ -0,0 +1,32 @@
+import typing as t
+from collections import Counter
+
+from src.utils.binary_tree import TreeNode
+
+
+class Solution:
+    def findMode(self, root: TreeNode | None) -> list[int]:
+        counter: t.Counter[int] = Counter()
+
+        def dfs(node: TreeNode | None) -> None:
+            if node is None:
+                return
+
+            counter[node.val] += 1
+
+            dfs(node.left)
+            dfs(node.right)
+
+        dfs(root)
+
+        result: list[int] = []
+
+        [(_, most_common)] = counter.most_common(1)
+
+        for x, count in counter.most_common():
+            if count == most_common:
+                result.append(x)
+            else:
+                break
+
+        return result

tests/test_find_mode_in_binary_search_tree.py

@@ -0,0 +1,16 @@
+import pytest
+
+from src.find_mode_in_binary_search_tree import Solution
+from src.utils.binary_tree import list_to_tree
+
+
+@pytest.mark.parametrize(
+    "in_list,expected",
+    (
+        ([1, None, 2, 2], [2]),
+        ([0], [0]),
+    ),
+)
+def test_solution(in_list, expected):
+    root = list_to_tree(in_list)
+    assert Solution().findMode(root) == expected