LCA in BinarySearchTree

Author: naina024

Trees/P07_LCAinBST.py

@@ -0,0 +1,43 @@
+# Lowest Common Ancestor in Binary search tree
+
+class node:
+    def __init__(self,key):
+        self.key=key
+        self.left=None
+        self.right=None
+
+def lca(root,n1,n2):
+    if root is None:
+        return None
+
+    if root.key<n1 and root.key<n2:
+        return lca(root.right,n1,n2)
+
+    if root.key>n1 and root.key>n2:
+        return lca(root.left,n1,n2)
+
+    return root
+
+# Consider the following BST
+
+#                  8
+#               /     \
+#             3         11
+#           /   \     /   \
+#          2     6   10    13
+#              /   \      /
+#             5     7    12
+
+# Create BST
+root = node(8)
+l = root.left = node(3)
+r = root.right = node(11)
+r.left = node(10)
+r.right = node(13)
+r.right.left = node(12)
+l.left = node(2)
+l.right = node(6)
+l.right.left = node(5)
+l.right.right = node(7)
+
+print(lca(root,2,7).key) # ouputs '3'