add py3/node soln

0669_trim-a-binary-search-tree/python3/solution.py

@@ -0,0 +1,37 @@
+# Time: O(N)
+# Space: O(N) due to call stack
+
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def trimBST(self, root: Optional[TreeNode], low: int, high: int) -> Optional[TreeNode]:
+        # Recursion approach
+        
+        def trim(node):
+            # Base case
+            if node is None:
+                return None
+            
+            if node.val < low:
+                # Cause everything to the left will be
+                # less than `low` and hence trimmed
+                return trim(node.right)
+            
+            elif node.val > high:
+                # Cause everything to the right will be
+                # greater than `high` and hence trimmed
+                return trim(node.left)
+            
+            else:
+                # `node.val` is between [low, high] so
+                # just need to trim their left and right
+                # subtrees
+                node.left = trim(node.left)
+                node.right = trim(node.right)
+                return node
+            
+        return trim(root)