From 7a277c6ccc61548a15c440530f5b938f8378500e Mon Sep 17 00:00:00 2001
From: Pavel Karateev <lancelote.du.lac@gmail.com>
Date: Mon, 4 Nov 2024 21:56:38 +0100
Subject: [PATCH] solve "106. Construct Binary Tree from Inorder and Postorder
 Traversal"

---
 ...ee_from_inorder_and_postorder_traversal.py | 32 +++++++++++++++++++
 ...ee_from_inorder_and_postorder_traversal.py | 18 +++++++++++
 2 files changed, 50 insertions(+)
 create mode 100644 src/construct_binary_tree_from_inorder_and_postorder_traversal.py
 create mode 100644 tests/test_construct_binary_tree_from_inorder_and_postorder_traversal.py

diff --git a/src/construct_binary_tree_from_inorder_and_postorder_traversal.py b/src/construct_binary_tree_from_inorder_and_postorder_traversal.py
new file mode 100644
index 0000000..70f279a
--- /dev/null
+++ b/src/construct_binary_tree_from_inorder_and_postorder_traversal.py
@@ -0,0 +1,32 @@
+from src.utils.binary_tree import TreeNode
+
+
+class Solution:
+    def buildTree(
+        self, inorder: list[int], postorder: list[int]
+    ) -> TreeNode | None:
+        n = len(inorder)
+        postorder_idx = n - 1
+
+        def dfs(left: int, right: int) -> TreeNode | None:
+            nonlocal postorder_idx
+
+            if left > right:
+                return None
+
+            value = postorder[postorder_idx]
+            inorder_idx = val_to_inorder_idx[value]
+            node = TreeNode(value)
+
+            postorder_idx -= 1
+
+            node.right = dfs(inorder_idx + 1, right)
+            node.left = dfs(left, inorder_idx - 1)
+
+            return node
+
+        val_to_inorder_idx: dict[int, int] = {}
+        for idx, val in enumerate(inorder):
+            val_to_inorder_idx[val] = idx
+
+        return dfs(0, n - 1)
diff --git a/tests/test_construct_binary_tree_from_inorder_and_postorder_traversal.py b/tests/test_construct_binary_tree_from_inorder_and_postorder_traversal.py
new file mode 100644
index 0000000..0353806
--- /dev/null
+++ b/tests/test_construct_binary_tree_from_inorder_and_postorder_traversal.py
@@ -0,0 +1,18 @@
+import pytest
+
+from src.construct_binary_tree_from_inorder_and_postorder_traversal import (
+    Solution,
+)
+from src.utils.binary_tree import tree_to_list
+
+
+@pytest.mark.parametrize(
+    "inorder,postorder,expected_out_list",
+    (
+        ([9, 3, 15, 20, 7], [9, 15, 7, 20, 3], [3, 9, 20, None, None, 15, 7]),
+        ([-1], [-1], [-1]),
+    ),
+)
+def test_solution(inorder, postorder, expected_out_list):
+    out_tree = Solution().buildTree(inorder, postorder)
+    assert tree_to_list(out_tree) == expected_out_list