Cycle Detection Directed

Problem

Decide whether a directed graph with n nodes contains a directed cycle.

Use three colors: white (unvisited), gray (on the current DFS stack), and black (finished). An edge into a gray node closes a cycle. edges is a list of [u, v] pairs.

Hint

A back edge to a node still on the recursion stack proves a directed cycle.

Test cases

case 1

in: [4,[[0,1],[1,2],[2,3]]]

expected: false

case 2

in: [3,[[0,1],[1,2],[2,0]]]

expected: true

case 3

in: [3,[[0,1],[0,2],[1,2]]]

expected: false

case 4

in: [1,[[0,0]]]

expected: true

case 5

in: [3,[[0,1],[1,2]]]

expected: false

Starter codePython

def has_cycle_directed(n, edges):
    # Your code here
    pass

5 test cases · run your code against them in the editor