# Convert binary tree to its Sum tree

Objective: Given a binary tree, write an algorithm to convert it into its Sum tree.

What is Sum tree: Sum tree of a binary tree, is a tree where each node in the converted tree will contains the sum of the left and right sub trees in the original tree.

Example: Approach:

1. Recursively calculate the left sum from left sum tree.
2. Recursively calculate the right sum from right tree.
3. prepare the return root.data + left sum + right sum.
4. Update the root data as root.data = left sum + right sum.
5. update the newRoot = root.
6. See the code for better understanding.

Complete Code:

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 public class TreeToSumTree { static Node newRoot; public int SumTree(Node root){ if(root!=null){ int left = SumTree(root.left);//take the left tree sum int right = SumTree(root.right);//take the right tree sum int retData = root.data+left+right; // return data left+right+root root.data = left+right; //update the root with left + right newRoot = root; //update the new root return retData; //return } return 0; } public void display(Node root){ if(root!=null){ display(root.left); System.out.print(root.data + " " ); display(root.right); } } public static void main(String args[]){ Node root = new Node(5); root.left = new Node(–1); root.right = new Node(3); root.left.left = new Node(–2); root.left.right = new Node(4); root.right.left = new Node(–6); root.right.right = new Node(10 ); TreeToSumTree t = new TreeToSumTree(); System.out.print("Original Tree: "); t.display(root); System.out.print("\nSum tree: "); t.SumTree(root); //Print the new tree t.display(newRoot); } } class Node{ int data; Node left; Node right; public Node(int data){ this.data = data; } }

Output:

```Original Tree: -2  -1  4  5  -6  3  10
Sum tree: 0  2  0  8  0  4  0
```

### 2 thoughts on “Convert binary tree to its Sum tree”

1. why do u need to set the newRoot in line13? you are not changing any node pointers in the SumTree method. looks like an unnecessary line of code that really does nothing.

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