private void findInChild(Node root, int k){
        if(root == null){
            return;
        }
        if(k == 0){
            System.out.println(root.data);
        }
        findInChild(root.left, k-1);
        findInChild(root.right, k-1);
    }
http://www.geeksforgeeks.org/print-nodes-distance-k-given-node-binary-tree/
Test case 
k should not be negative
k could be very big number which means nothing was found
dest might/might not exists in the tree
root could be null
src/com/interview/tree/NodesAtDistanceK.java