Add delete method for AVL tree

README.md

@@ -7,10 +7,10 @@ Please ask questions in [Issues](https://github.com/msambol/youtube/issues).
 * [CS Tutorials](https://www.youtube.com/playlist?list=PL9xmBV_5YoZPKwb4XPB1sG7S6kNpN9JJo) – all of my computer science tutorials in one playlist
 * [Big-O Notation](https://www.youtube.com/playlist?list=PL9xmBV_5YoZMxejjIyFHWa-4nKg6sdoIv)
 * [Data Structures](https://www.youtube.com/playlist?list=PL9xmBV_5YoZO2D89q42-y8voxIJKpB4oR)
-* [Maximum Flow Algos](https://www.youtube.com/playlist?list=PL9xmBV_5YoZPxifnyXjQVU1bhU4b4_Ts2)
 * [Minimum Spanning Trees](https://www.youtube.com/playlist?list=PL9xmBV_5YoZObEi3Hf6lmyW-CBfs7nkOV)
-* [Search Algos](https://www.youtube.com/playlist?list=PL9xmBV_5YoZMIAJn8M6At9CjZ0Wu0B31d)
 * [Shortest Path Algos](https://www.youtube.com/playlist?list=PL9xmBV_5YoZO-Y-H3xIC9DGSfVYJng9Yw)
+* [Maximum Flow Algos](https://www.youtube.com/playlist?list=PL9xmBV_5YoZPxifnyXjQVU1bhU4b4_Ts2)
+* [Search Algos](https://www.youtube.com/playlist?list=PL9xmBV_5YoZMIAJn8M6At9CjZ0Wu0B31d)
 * [Sort Algos](https://www.youtube.com/playlist?list=PL9xmBV_5YoZOZSbGAXAPIq1BeUf4j20pl)
 * [Tree Traversal Algos](https://www.youtube.com/playlist?list=PL9xmBV_5YoZO1JC2RgEi04nLy6D-rKk6b)
 * [Red-Black Trees](https://www.youtube.com/playlist?list=PL9xmBV_5YoZNqDI8qfOZgzbqahCUmUEin)

trees/README.md

@@ -53,6 +53,7 @@
 * [Playlist]()
 * Videos: [Intro & Search]() | [Insertions]() | [Deletions]()
 * h/t **Shivali Bhadaniya** – [Article](https://favtutor.com/blogs/avl-tree-python) | [LinkedIn](https://www.linkedin.com/in/shivali-bhadaniya-76932a192/)
+* h/t **Programiz** – [AVL Tree](https://www.programiz.com/dsa/avl-tree)
 
 ```
 ❯ python avl_tree.py
@@ -77,6 +78,25 @@ Level-order traversal with height and balance factor:
 
 Search for 125: 125
 Search for 1: not found
+
+After deleting 120:
+
+Level-order traversal:
+50 25 75 15 35 60 90 10 68 83 125 100 
+
+Level-order traversal with height and balance factor:
+50:  h = 5, bf = -1
+25:  h = 3, bf = 1
+75:  h = 4, bf = -1
+15:  h = 2, bf = 1
+35:  h = 1, bf = 0
+60:  h = 2, bf = -1
+90:  h = 3, bf = -1
+10:  h = 1, bf = 0
+68:  h = 1, bf = 0
+83:  h = 1, bf = 0
+125: h = 2, bf = 1
+100: h = 1, bf = 0
 ```
 
 ### B-trees

trees/avl_tree.py

@@ -20,6 +20,9 @@ def get_height(self, node):
     def get_balance_factor(self, node):
         return 0 if not node else (self.get_height(node.left) - self.get_height(node.right))
 
+    def get_min_node(self, node):
+        return node if not node or not node.left else self.get_min_node(node.left)
+
     # O(logn)
     def search(self, key):
         x = self.root
@@ -60,8 +63,51 @@ def insert(self, root, key):
 
         return root
 
-    def delete(self, key):
-        pass
+    # O(logn)
+    def delete(self, root, key):
+        if not root:
+            return root
+        elif key < root.key:
+            root.left = self.delete(root.left, key)
+        elif key > root.key:
+            root.right = self.delete(root.right, key)
+        else:
+            if not root.left:
+                temp = root.right
+                root = None
+                return temp 
+            elif not root.right:
+                temp = root.left
+                root = None 
+                return temp 
+            # find inorder successor
+            temp = self.get_min_node(root.right)
+            root.key = temp.key
+            root.right = self.delete(root.right, temp.key)
+
+        if root is None:
+            return root
+
+        root.height = 1 + max(self.get_height(root.left), self.get_height(root.right))
+
+        # Update the balance factor and balance the tree
+        bf = self.get_balance_factor(root)
+
+        if bf > 1 and self.get_balance_factor(root.left) >= 0:
+            return self.right_rotate(root)
+
+        if bf < -1 and self.get_balance_factor(root.right) <= 0:
+            return self.left_rotate(root)
+
+        if bf > 1 and self.get_balance_factor(root.left) < 0:
+            root.left = self.left_rotate(root.left)
+            return self.right_rotate(root)
+
+        if bf < -1 and self.get_balance_factor(root.right) > 0:
+            root.right = self.right_rotate(root.right)
+            return self.left_rotate(root)
+
+        return root
 
     # O(1)
     def left_rotate(self, node):
@@ -134,7 +180,9 @@ def main():
 
     result = avl.search(1)
     print(f'Search for 1: {print_search_result(result)}')
-
-    return avl
+
+    avl.root = avl.delete(avl.root, 120)
+    print('\nAfter deleting 120:')
+    avl.print_tree()
 
 main()