solution.cpp

class Solution
{
public:
    bool canFinish(int n, vector<vector<int>> &prerequisites)
    {
        vector<vector<int>> adj(n);
        vector<int> indegree(n, 0);

        // Build graph
        for (auto &p : prerequisites)
        {
            adj[p[1]].push_back(p[0]);
            indegree[p[0]]++;
        }

        queue<int> q;

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

        int count = 0;

        // BFS (Topological Sort)
        while (!q.empty())
        {
            int node = q.front();
            q.pop();
            count++;

            for (int neighbor : adj[node])
            {
                indegree[neighbor]--;
                if (indegree[neighbor] == 0)
                {
                    q.push(neighbor);
                }
            }
        }

        // If all nodes processed, no cycle
        return count == n;
    }
};