| 4 | |
| 5 | class Solution { |
| 6 | public boolean canFinish(int numCourses, int[][] prerequisites) { |
| 7 | // Build graph |
| 8 | List<Integer>[] graph = new ArrayList[numCourses]; |
| 9 | for (int i = 0; i < numCourses; i++) { |
| 10 | graph[i] = new ArrayList<>(); |
| 11 | } |
| 12 | int[] indegree = new int[numCourses]; |
| 13 | |
| 14 | for (int[] pre : prerequisites) { |
| 15 | graph[pre[1]].add(pre[0]); |
| 16 | indegree[pre[0]]++; |
| 17 | } |
| 18 | |
| 19 | // BFS - Kahn's algorithm |
| 20 | Queue<Integer> queue = new LinkedList<>(); |
| 21 | for (int i = 0; i < numCourses; i++) { |
| 22 | if (indegree[i] == 0) { |
| 23 | queue.add(i); |
| 24 | } |
| 25 | } |
| 26 | |
| 27 | int count = 0; |
| 28 | while (!queue.isEmpty()) { |
| 29 | int course = queue.poll(); |
| 30 | count++; |
| 31 | |
| 32 | for (int neighbor : graph[course]) { |
| 33 | indegree[neighbor]--; |
| 34 | if (indegree[neighbor] == 0) { |
| 35 | queue.add(neighbor); |
| 36 | } |
| 37 | } |
| 38 | } |
| 39 | |
| 40 | return count == numCourses; |
| 41 | } |
| 42 | } |