Java program to find the sum of all the nodes of a binary tree

In this program, we need to calculate the sum of nodes present in the binary tree. First, we will traverse through the left sub-tree and calculate the sum of nodes present in the left sub-tree. Similarly, we calculate the sum of nodes present in the right sub-tree and calculate total sum by adding the root?s data.

For the given tree, sum of nodes of the binary tree will be 1 + 2 + 5 + 8 + 6 + 9 = 31.

Algorithm

Define Node class which has three attributes namely: data left and right. Here, left represents the left child of the node and right represents the right child of the node.
When a node is created, data will pass to data attribute of the node and both left and right will be set to null.
Define another class which has an attribute root.
- Root represents the root node of the tree and initialize it to null.

a. calculateSum() will calculate the sum of nodes present in the binary tree:

It checks whether the root is null, which means that the tree is empty.
If the tree is not empty, traverse through left subtree, calculate the sum of nodes and store it in sumLeft.
Then, traverse through the right subtree, calculate the sum of nodes and store it in sumRight.
Finally, calculate total sum = temp.data + sumLeft + sumRight.

Program:

public class SumOfNodes {

      //Represent the node of binary tree
        public static class Node{
        int data;
        Node left;
        Node right;

        public Node(int data){
            //Assign data to the new node, set left and right children to null
            this.data = data;
            this.left = null;
            this.right = null;
        }
      }

      //Represent the root of binary tree
      public Node root;

      public SumOfNodes(){
        root = null;
      }

      //calculateSum() will calculate the sum of all the nodes present in the binary tree
      public int calculateSum(Node temp){
        int sum, sumLeft, sumRight;
        sum = sumRight = sumLeft = 0;

        //Check whether tree is empty
        if(root == null) {
            System.out.println("Tree is empty");
            return 0;
        }
        else {
            //Calculate the sum of nodes present in left subtree
            if(temp.left != null)
                sumLeft = calculateSum(temp.left);

            //Calculate the sum of nodes present in right subtree
            if(temp.right != null)
                sumRight = calculateSum(temp.right);

            //Calculate the sum of all nodes by adding sumLeft, sumRight and root node's data
            sum = temp.data + sumLeft + sumRight;
            return sum;
        }
      }

      public static void main(String[] args) {

        SumOfNodes bt = new SumOfNodes();
        //Add nodes to the binary tree
        bt.root = new Node(5);
        bt.root.left = new Node(2);
        bt.root.right = new Node(9);
        bt.root.left.left = new Node(1);
        bt.root.right.left = new Node(8);
        bt.root.right.right = new Node(6);

        //Display the sum of all the nodes in the given binary tree
        System.out.println("Sum of all nodes of binary tree: " + bt.calculateSum(bt.root));
      }
    }

Output: