Detecting all circles in a graph

Question

I have a directed graph stored in a Map data structure, where the key is the node\'s ID and the [value] is the array of the nodeIds of the nodes which are pointed by the key no

Answer 1

Since a circle in a directed graph represents a strongly connected component, you can use any of the algorithms referenced on the wikipedia page for finding strongly connected components https://en.wikipedia.org/wiki/Strongly_connected_component - for instance Tarjan's algorithm which is based on depth-first search: https://en.wikipedia.org/wiki/Tarjan%27s_strongly_connected_components_algorithm

Edit: It is possible that a strongly connected component contains multiple circles that share nodes with each other. So, a manual checking of each component must follow, but should be easy.