Create construct-binary-search-tree-from-preorder-traversal.py

Author: kamyu104

Python/construct-binary-search-tree-from-preorder-traversal.py

@@ -0,0 +1,30 @@
+# Time:  O(n)
+# Space: O(h)
+
+# Definition for a binary tree node.
+class TreeNode(object):
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None
+
+
+class Solution(object):
+    def bstFromPreorder(self, preorder):
+        """
+        :type preorder: List[int]
+        :rtype: TreeNode
+        """
+        def bstFromPreorderHelper(preorder, left, right, index):
+            if index[0] == len(preorder) or \
+               preorder[index[0]] < left or \
+               preorder[index[0]] > right:
+                return None
+
+            root = TreeNode(preorder[index[0]])
+            index[0] += 1
+            root.left = bstFromPreorderHelper(preorder, left, root.val, index)
+            root.right = bstFromPreorderHelper(preorder, root.val, right, index)
+            return root
+        
+        return bstFromPreorderHelper(preorder, float("-inf"), float("inf"), [0])