solution.java

import java.util.*;

class Solution {
    public boolean canFinish(int n, int[][] prerequisites) {
        List<List<Integer>> adj = new ArrayList<>();
        for (int i = 0; i < n; i++)
            adj.add(new ArrayList<>());

        int[] indegree = new int[n];

        // Build graph
        for (int[] p : prerequisites) {
            adj.get(p[1]).add(p[0]);
            indegree[p[0]]++;
        }

        Queue<Integer> q = new LinkedList<>();

        // Add nodes with 0 indegree
        for (int i = 0; i < n; i++) {
            if (indegree[i] == 0)
                q.offer(i);
        }

        int count = 0;

        // BFS
        while (!q.isEmpty()) {
            int node = q.poll();
            count++;

            for (int nei : adj.get(node)) {
                indegree[nei]--;
                if (indegree[nei] == 0)
                    q.offer(nei);
            }
        }

        return count == n;
    }
}