### Python program to merge two binary trees by doing node sum using recursion

Description:
To merge two binary trees using recursion, the rule is that if two nodes overlap, then sum nodes value up as the new value of the merged node. Otherwise , the non-null node will be used as the node of the new tree.

Example:
Input:
Tree 1                                         Tree 2

Output:
Merged Tree

So the algorithm for recursive approach is :
Traverse the tree in pre-order fashion.
Check if both the tree nodes are null, if not then update the value
Recur for left sub trees
Recur for right sub trees
Return root of updated tree

Program:
class newNode: def __init__(self, data): self.data = data self.left = self.right = None # Given a binary tree, prits nodes in inorder def inorder(node): if (not node): return # first recur on left child inorder(node.left) # then print the data of node print(node.data, end = " ") # now recur on right child inorder(node.right) # Function to merge given twobinary trees def MergeTrees(t1, t2): if (not t1): return t2 if (not t2): return t1 t1.data += t2.data t1.left = MergeTrees(t1.left, t2.left) t1.right = MergeTrees(t1.right, t2.right) return t1 # Driver code if __name__ == '__main__': # Let us construct the first Binary Tree # 1 # / \ # 2 3 # / \ \ # 4 5 6 root1 = newNode(1) root1.left = newNode(2) root1.right = newNode(3) root1.left.left = newNode(4) root1.left.right = newNode(5) root1.right.right = newNode(6) # Let us construct the second Binary Tree # 4 # / \ # 1 7 # / / \ # 3 2 6 root2 = newNode(4) root2.left = newNode(1) root2.right = newNode(7) root2.left.left = newNode(3) root2.right.left = newNode(2) root2.right.right = newNode(6) root3 = MergeTrees(root1, root2) print("The Merged Binary Tree is:") inorder(root3)

Output:

The Merged Binary Tree is:
7 3 5 5 2 10 12
>>>

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