detectCycle.cpp

#include<bits/stdc++.h>
using namespace std;
class Graph {

	int  v;
	list<int> *l;
public:
	Graph(int v) {
		this->v = v;
		l = new list<int>[v];
	}
	void addEdge(int x, int y) {
		l[x].push_back(y);
	}

	bool cycle_helper(int src, bool *visited, bool *stack) {
		visited[src] = true;
		stack[src] = true;

		for (auto nbr : l[src]) {
			if (stack[nbr] == true) {
				return true;
			} else if (!visited[nbr]) {
				bool found = cycle_helper(nbr, visited, stack);
				if (found) {
					return true;
				}
			}
		}
		stack[src] = false;
		return false;
	}
	bool dfs() {
		bool *visited = new bool[v];
		bool *stack = new bool[v];

		for (int i = 0; i < v; i++) {
			visited[i] = stack[i] = false;
		}

		return cycle_helper(0, visited, stack);
	}
};
int main() {

	Graph g(7);
	g.addEdge(0, 1);
	g.addEdge(1, 2);
	g.addEdge(2, 3);
	g.addEdge(3, 4);
	g.addEdge(4, 5);
	g.addEdge(1, 5);
	g.addEdge(5, 6);
	//g.addEdge(4,2);

	if (g.dfs()) {
		cout << "Yes" << endl;
	} else {
		cout << "No" << endl;
	}
	return 0;
}