Given a directory, print all files and folders present in directory tree rooted with given directory.
We can iteratively traverse directory in BFS using below steps. We create an empty queue and
we first enqueue given directory path. We run a loop while queue is not empty. We dequeue an
item from queue. If the popped item is a directory, get list of all files and directories present in
it, add each directory to the queue. If the popped item is a file, we print its name.