Solve : Construct Binary Tree from Preorder and Inorder Traversal

Author: printjin-gmailcom

construct-binary-tree-from-preorder-and-inorder-traversal/printjin-gmailcom.py

@@ -0,0 +1,14 @@
+class Solution:
+    def buildTree(self, preorder, inorder):
+        inorder_index_map = {val: idx for idx, val in enumerate(inorder)}
+        def build(pre_left, pre_right, in_left, in_right):
+            if pre_left > pre_right:
+                return None
+            root_val = preorder[pre_left]
+            root = TreeNode(root_val)
+            in_root_idx = inorder_index_map[root_val]
+            left_size = in_root_idx - in_left
+            root.left = build(pre_left + 1, pre_left + left_size, in_left, in_root_idx - 1)
+            root.right = build(pre_left + left_size + 1, pre_right, in_root_idx + 1, in_right)
+            return root
+        return build(0, len(preorder) - 1, 0, len(inorder) - 1)