Update README.md

dynamic_programming/README.md

@@ -154,6 +154,47 @@ def climb_stairs_memoization(n: int) -> int:
 
 <br>
 
+* another good examples is calculating all possible subnodes in a tree:
+
+<br>
+
+```python
+class Node:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+
+def all_possible_bst(start, end, memo):
+
+        result = []
+        if start > end:
+            return result
+        
+        if (start, end) in memo:
+            return memo[(start, end)]
+
+        for i in range(start, end + 1):
+            left = all_possible_bst(start, i - 1, memo)
+            right = all_possible_bst(i + 1, end, memo)
+
+            for l in left:
+                for r in right:
+                    result.append(Node(i, l, r))
+
+        memo[(start, end)] = result
+        return result
+
+
+def generate_trees(n):
+
+    memo = {}
+    return all_possible_bst(1, n, memo)
+```
+
+<br>
+
 ----
 
 ### time complexity
@@ -208,3 +249,5 @@ def backtrack(candidate):
             remove(next_candidate)
 ````
 
+<br>
+