Count in-degrees — practice exercise

What you'll be asked to do

1. 1.Count in-degreesexercise · easy · 10 min

   Count how many edges point at node 2.

   Passes when: #out should show indegree 1.

2. 2.Order a simple chainexercise · easy · 10 min · practice plan

   Produce a topological order for a chain and join it.

   Passes when: #out should show 0-1-2.

3. 3.Detect a cycleexercise · easy · 10 min · practice plan

   Report that a two-node cycle has no valid ordering.

   Passes when: #out should show cycle found.

4. 4.Find the starting nodesexercise · easy · 10 min · practice plan

   Count how many nodes have no incoming edge.

   Passes when: #out should show one start.

5. 5.Several valid ordersexercise · medium · 10 min · practice plan

   Report whether more than one ordering can exist when two nodes are ready.

   Passes when: #out should show many orders.

6. 6.Fix in-degree counting the sourcebug fix · easy · 8 min

   The first element of an edge is where it comes from, not where it points.

   Passes when: #out should show indegree 1.

7. 7.Fix the queue seeded with everythingbug fix · easy · 8 min · practice plan

   Starting with every node ignores the dependencies entirely.

   Passes when: #out should show 0-1-2.

8. 8.Fix the cycle reported as an orderbug fix · medium · 8 min · practice plan

   A shorter output than the node count means no ordering exists.

   Passes when: #out should show cycle found.

9. 9.Fix the decrement compared before subtractingbug fix · easy · 8 min · practice plan

   Using a post-decrement checks the old value and enqueues too early.

   Passes when: #out should show 0-1-2.

10. 10.Fix the start count including targetsbug fix · easy · 8 min · practice plan

    Nodes with incoming edges are not starting points.

    Passes when: #out should show one start.

Between them these tasks cover In-degree, Kahn's algorithm and Cycle detection.

Looking for a different chapter? See every practice set, or switch to the interview theory questions.