Adding Simple Solution for Problem - 105 - Construct BT Preorder Inorder Traversal

Author: Vanditg

Construct_BT_Preorder_Inorder_Traversal/SimpleSolution.py

@@ -0,0 +1,42 @@
+##==================================
+## Leetcode
+## Student: Vandit Jyotindra Gajjar
+## Year: 2020
+## Problem: 105
+## Problem Name: Construct Binary Tree from Preorder and Inorder Traversal
+##===================================
+#
+#Given preorder and inorder traversal of a tree, construct the binary tree.
+#
+#Note:
+#You may assume that duplicates do not exist in the tree.
+#
+#For example, given
+#
+#preorder = [3,9,20,15,7]
+#inorder = [9,3,15,20,7]
+#Return the following binary tree:
+#
+#    3
+#   / \
+#  9  20
+#    /  \
+#   15   7
+class Solution:
+    def buildTree(self, preorder, inorder):
+        l_preorder = len(preorder)	#Initialize l_preorder by finding length of preorder
+        l_inorder = len(inorder)	#Initialize l_inorder by finding length of inorder
+        if l_preorder != l_inorder:	#Condition-check:	If l_preorder and l_inorder are not the same 
+            return None	#We return none as the tree is different 
+        if preorder is None:	#Condition-check: If preorder is empty
+            return None	#We return none as preorder is different
+        if inorder is None:	#Condition-check: If inorder is empty
+            return None	#We return none as inorder is different
+        if l_preorder == 0:	#If length of preorder is zero
+            return None	#We return none as preorder is different
+        root = TreeNode(preorder[0])	#Initialize root by taking first value from preorder
+        root_index = inorder.index(root.val)	#Initialize root_index by taking index from inorder's root
+        root.left = self.buildTree(preorder[1:root_index + 1], inorder[:root_index])	#Initialize root.left by using recursion
+        root.right = self.buildTree(preorder[root_index + 1:], inorder[root_index + 1:])	#Initialize root.right by using recursion 
+        return root	#We return root after no value is present in preorder or inorder		
+