Print nodes at k level from the root in a binary tree
[et_pb_section admin_label="section"][et_pb_row admin_label="row"][et_pb_column type="4_4"][et_pb_text admin_label="Text" background_layout="light" text_orientation="left" use_border_color="off" border_color="#ffffff" border_style="solid"]
Given a binary tree, level k, print all the nodes at level k.
For example, 4, 7, 8 are at level 2.
1
/ \
2 3
/ \ /
4 7 8