Amarkant814
diff --git a/‎09 September Challenge 2021/02_uniqueBST2.py
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+24Lines changed: 24 additions & 0 deletions b/‎09 September Challenge 2021/02_uniqueBST2.py
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+24Lines changed: 24 additions & 0 deletions
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+# 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 generateTrees(self, n: int) -> List[Optional[TreeNode]]:
+        @lru_cache(None)
+        def dfs(left, right):
+            if left > right: return [None]
+            if left == right: return [TreeNode(left)]
+            ans = []
+            for root in range(left, right+1):
+                leftNodes = dfs(left, root - 1)
+                rightNodes = dfs(root+1, right)
+                for leftNode in leftNodes:
+                    for rightNode in rightNodes:
+                        rootNode = TreeNode(root, leftNode, rightNode)
+                        ans.append(rootNode)
+            return ans
+        
+        return dfs(1, n)