One usage is through detecting cycles in a linked list
data structure. For example, a cycle (when a node points back to a previous node) begins at the last node of the linked list
in the example below.
xxxxxxxxxx
1 -- > 2 --> 3 --> 4
^ |
| |
<- - -
OUTPUT
:001 > Cmd/Ctrl-Enter to run, Cmd/Ctrl-/ to comment