Adding 0106 - Construct Binary Tree from Inorder and Postorder Traversal

LeetCode/0106_Construct_Binary_Tree_from_Inorder_and_Postorder_Traversal.py

@@ -0,0 +1,22 @@
+class Solution:
+ def buildTree(self, inorder: List[int], postorder: List[int]) -> TreeNode:
+ return self.helperFunc(inorder, postorder, 0, len(inorder)-1, len(postorder)-1)
+ def helperFunc(self, inorder: List[int], postorder: List[int], left: int, right: int, postIndex: int) -> TreeNode:
+ # checks if there is node required else puts null in the binary tree
+ if postIndex == -1:
+ return
+ # creating the root of the subtree from the value present at current postIndex
+ root = TreeNode(postorder[postIndex])
+ # we find the root's value in order to divide them into left and right subtree
+ x = 0
+ for i in range(len(inorder)):
+ if root.val == inorder[i]:
+ x = i
+ # finding corresponding values that are roots for left and right subtrees or assign -1
+ right_post = -1 if abs(right - x) == 0 else postIndex - 1
+ left_post = -1 if abs(left - x) == 0 else postIndex -1 - abs(right - x)
+ # calling recursively helperFunc for left and right subtrees
+ root.left = self.helperFunc(inorder, postorder, left, x-1, left_post)
+ root.right = self.helperFunc(inorder, postorder, x+1, right, right_post)
+ return root
+