https://leetcode.com/problems/recover-a-tree-from-preorder-traversal

hard/recover_a_tree_from_preorder_traversal.py

@@ -0,0 +1,42 @@
+# https://leetcode.com/problems/recover-a-tree-from-preorder-traversal
+
+from typing import Optional
+
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+class Solution:
+    def recoverFromPreorder(self, traversal: str) -> Optional[TreeNode]:
+        i = 0
+        def recurse(level, curr: TreeNode):
+            nonlocal i
+            val = []
+            while i < len(traversal) and traversal[i] != '-':
+                val.append(traversal[i])
+                i += 1
+            if len(val) > 0:
+                curr.val = int(''.join(val))
+
+            next_level = 0
+            while i + next_level < len(traversal) and traversal[i + next_level] == '-':
+                next_level += 1
+            if next_level == level + 1:
+                i += next_level
+                curr.left = TreeNode()
+                recurse(next_level, curr.left)
+
+            next_level = 0
+            while i + next_level < len(traversal) and traversal[i + next_level] == '-':
+                next_level += 1
+            if next_level == level + 1:
+                i += next_level
+                curr.right = TreeNode()
+                recurse(next_level, curr.right)
+
+        result = TreeNode()
+        recurse(0, result)
+        return result
+