### Question

In the context of this exercise, what is a cycle in a graph?

### Answer

A cycle is a path of vertices and edges where you can start from a vertex and follow the path all the way back to that starting vertex. These cycles only occur for directed graphs.

For example, the following graph will contain a cycle:

```
graph = {
'A': ['B'],
'B': ['C'],
'C': ['A']
}
```

In this graph, there is a cycle formed by the path `A -> B -> C`

, back to `A`

.

Cycles are sometimes harmless, but other times they can cause bugs in graph algorithms due to infinite looping.