Create P06_LCAinBinaryTree.py

Trees/P06_LCAinBinaryTree.py

@@ -0,0 +1,48 @@
+# LCA - least common ancestor
+# The lowest common ancestor of two nodes n1 and n2 is the lowest node in tree that has both n1 and n2 as descendants.
+
+
+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 or root.key == n2:
+        return root
+
+    left = lca(root.left, n1, n2)
+    right = lca(root.right, n1, n2)
+
+    if left and right:
+        return root
+
+    return left if left else right
+
+
+# Consider the following binary tree
+
+#                  3
+#               /     \
+#             6         8
+#           /   \         \
+#          2     11        13
+#              /    \      /
+#             9      5    7
+
+# Create binary tree
+root=node(3)
+l = root.left = node(6)
+r = root.right = node(8)
+r.right = node(13)
+r.right.left = node(7)
+l.left = node(2)
+l.right = node(11)
+l.right.left = node(9)
+l.right.right = node(5)
+
+print(lca(root, 2, 5).key)  # outputs '6'