Adding Efficient Solution for Problem - 235 - Lowest Ancestor of BST

Author: Vanditg

Lowest_Ancestor_BST/EfficientSolution.py

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+##==================================
+## Leetcode
+## Student: Vandit Jyotindra Gajjar
+## Year: 2020
+## Problem: 230
+## Problem Name: Kth Smallest Element in a BST    
+##===================================
+#Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.
+#
+#According to the definition of LCA on Wikipedia: 
+#“The lowest common ancestor is defined between two nodes p and q as the 
+#lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).”
+#
+#Given binary search tree:  root = [6,2,8,0,4,7,9,null,null,3,5]
+#
+#Example 1:
+#
+#Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8
+#Output: 6
+#Explanation: The LCA of nodes 2 and 8 is 6.
+#Example 2:
+#
+#Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4
+#Output: 2
+#Explanation: The LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.
+class Solution:
+    def lowestCommonAncestor(self, root, p, q):
+        if (p.val < root.val and q.val < root.val):	#Condition-check: If the values of p and q is in the left subtree
+            return self.lowestCommonAncestor(root.left, p, q)	#Using recursion gives search for the left subtree and return the lowest ancestor
+        elif (p.val > root.val and q.val > root.val):	#Condition-check: If the values of p and q is in the right subtree
+            return self.lowestCommonAncestor(root.right, p, q)	#Using recursion gives search for the right subtree and return the lowest ancestor
+        else:	#Condition-check: Else
+            return root	#We simply return root value