Build-BinTree-from-PreInorderTraversal.py

def buildTree(self, preorder: List[int], inorder: List[int]) -> TreeNode:
        
        if len(inorder) < 1:
            return None
        
        root = TreeNode(preorder[0])
        
        rootindex = inorder.index(root.val)
        
        lefttree = inorder[:rootindex]
        
        righttree = inorder[rootindex+1:]
        
        preorder.remove(root.val)
            
        root.left = self.buildTree(preorder,lefttree)
        root.right = self.buildTree(preorder, righttree)
                
        return root
		
# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def mergeTrees(self, root1: TreeNode, root2: TreeNode) -> TreeNode:
        
        def buildTree(r1,r2):
            nxtNode = TreeNode()
            
            if not r1 and not r2:
                return 
                                    
            if r1 and r2:
                nxtNode = TreeNode(r1.val + r2.val)
            else:
                if not r1 and r2:
                    nxtNode = TreeNode(r2.val)
                elif r1 and not r2:
                    nxtNode = TreeNode(r1.val)
                else:
                    nxtNode = TreeNode(r1.val or r2.val)
            
            
            if r1.left and r2.left:
                nxtNode.left = buildTree(r1.left,r2.left)
            else:
                nxtNode.left = r1.left or r2.left
            
            if r1.right and r2.right:
                nxtNode.right = buildTree(r1.right, r2.right)
            else:
                nxtNode.right = r1.right or r2.right
                
            
            return nxtNode
            
        
        if not root1:
            return root2
        if not root2:
            return root1
        
        rtnode = TreeNode(root1.val + root2.val)
        print(rtnode)
        rtnode.left = buildTree(root1.left, root2.left)
        rtnode.right = buildTree(root1.right, root2.right)
        
        return rtnode