Course Schedule.cpp

class Solution {
public:
    bool canFinish(int numCourses, vector<vector<int>>& prerequisites) {
        vector<int> adj[numCourses];
        for (auto& pre : prerequisites) {
            adj[pre[1]].push_back(pre[0]);
        }


        
        vector<int>indegree(numCourses, 0);
        for (int i = 0; i < numCourses; i++) {
            for (auto it : adj[i]) {
                indegree[it]++;
            }
        }
        queue<int> q;
        for (int i = 0; i < numCourses; i++) {
            if (indegree[i] == 0) {
                q.push(i);
            }
        }
        vector<int> topo;
        while (!q.empty()) {
            int node = q.front();
            q.pop();
            topo.push_back(node);

            for (auto it : adj[node]) {
                indegree[it]--;
                if (indegree[it] == 0) {
                    q.push(it);
                }
            }
        }
        return topo.size() == numCourses;
    }
};