feat: [437] Path Sum III

src/binary_tree/dfs/path_sum_iii/solution.py

@@ -0,0 +1,25 @@
+from typing import Optional
+from collections import defaultdict
+from structures import TreeNode
+
+
+class Solution:
+    def dfs(self, root: Optional[TreeNode], current_sum: int, target_sum: int):
+        if root is None:
+            return 0
+
+        current_sum += root.val
+        count: int = self.cache[current_sum - target_sum]
+        self.cache[current_sum] += 1
+
+        count += self.dfs(root.left, current_sum, target_sum)
+        count += self.dfs(root.right, current_sum, target_sum)
+
+        self.cache[current_sum] -= 1
+
+        return count
+
+    def pathSum(self, root: Optional[TreeNode], targetSum: int) -> int:
+        self.cache = defaultdict(int)
+        self.cache[0] = 1
+        return self.dfs(root, 0, targetSum)

structures/tree.py

@@ -1,5 +1,10 @@
 class TreeNode:
-    def __init__(self, val: int = 0, left: int | None = None, right: int | None = None):
+    def __init__(
+        self,
+        val: int = 0,
+        left: "TreeNode | None" = None,
+        right: "TreeNode | None" = None,
+    ):
         self.val = val
         self.left = left
         self.right = right

tests/test_path_sum_iii.py

@@ -0,0 +1,16 @@
+import pytest
+from src.binary_tree.dfs.path_sum_iii.solution import Solution
+from test_utils import TreeBuilder
+
+
+@pytest.mark.parametrize(
+    "root, target_sum, expected",
+    [
+        ([10, 5, -3, 3, 2, None, 11, 3, -2, None, 1], 8, 3),
+        ([5, 4, 8, 11, None, 13, 4, 7, 2, None, None, 5, 1], 22, 3),
+    ],
+)
+def test_leaf_similar(root: list, target_sum: int, expected: int):
+    root = TreeBuilder.from_list(root)
+    solution = Solution()
+    assert solution.pathSum(root, target_sum) == expected