1 answers

```
import java.util.LinkedList;
import java.util.Queue;
public class DiffOddEven {
//Represent a 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 DiffOddEven(){
root = null;
}
//difference() will calculate the difference between sum of odd and even levels of binary tree
public int difference() {
int oddLevel = 0, evenLevel = 0, diffOddEven = 0;
//Variable nodesInLevel keep tracks of number of nodes in each level
int nodesInLevel = 0;
//Variable currentLevel keep track of level in binary tree
int currentLevel = 0;
//Queue will be used to keep track of nodes of tree level-wise
Queue<Node> queue = new LinkedList<Node>();
//Check if root is null
if(root == null) {
System.out.println("Tree is empty");
return 0;
}
else {
//Add root node to queue as it represents the first level
queue.add(root);
currentLevel++;
while(queue.size() != 0) {
//Variable nodesInLevel will hold the size of queue i.e. number of elements in queue
nodesInLevel = queue.size();
while(nodesInLevel > 0) {
Node current = queue.remove();
//Checks if currentLevel is even or not.
if(currentLevel % 2 == 0)
//If level is even, add nodes's to variable evenLevel
evenLevel += current.data;
else
//If level is odd, add nodes's to variable oddLevel
oddLevel += current.data;
//Adds left child to queue
if(current.left != null)
queue.add(current.left);
//Adds right child to queue
if(current.right != null)
queue.add(current.right);
nodesInLevel--;
}
currentLevel++;
}
//Calculates difference between oddLevel and evenLevel
diffOddEven = Math.abs(oddLevel - evenLevel);
}
return diffOddEven;
}
public static void main (String[] args) {
DiffOddEven bt = new DiffOddEven();
//Add nodes to the binary tree
bt.root = new Node(1);
bt.root.left = new Node(2);
bt.root.right = new Node(3);
bt.root.left.left = new Node(4);
bt.root.right.left = new Node(5);
bt.root.right.right = new Node(6);
//Display the difference between sum of odd level and even level nodes
System.out.println("Difference between sum of odd level and even level nodes: " + bt.difference());
}
}
```

**Output:**

```
Difference between sum of odd level and even level nodes: 11
```

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