https://medium.com/@Sazidz/how-to-detect-cycles-in-a-graph-6236e6eb750

1.cpp

// Holds the graph
map<char, vector<char>> graph;

// Status of each node - UNVISITED, VISITING, VISITED
map<char, int> status;

// This will denote whether the graph has cycles
bool hasCycles = false;

// Status codes
const int UNVISITED = 0;
const int VISITING = 1;
const int VISITED = 2;