public static void main(String args[]){
        BinaryTree bt = new BinaryTree();
        Node head = null;
        head = bt.addNode(3, head);
        head = bt.addNode(-6, head);
        head = bt.addNode(7, head);
        head = bt.addNode(-10, head);
        head = bt.addNode(-15, head);
        head = bt.addNode(-4, head);
        head = bt.addNode(4, head);
        head = bt.addNode(11, head);
        head = bt.addNode(-9, head);
            
        IsCompleteBinaryTree icbt = new IsCompleteBinaryTree();
        System.out.println(icbt.isComplete(head));
    }
http://www.geeksforgeeks.org/check-if-a-given-binary-tree-is-complete-tree-or-not/
Test cases:
A node with only right child
A node with only left child
A node with both left and right child
src/com/interview/tree/IsCompleteBinaryTree.java