CourseSchedule.cpp

class Solution {
public:
    bool canFinish(int numCourses, vector<vector<int>>& prerequisites) {
      int con=0,i,sz=prerequisites.size(),len,fron;
        vector<int>indegree(numCourses,0);
        vector<vector<int>>graph(numCourses);
        for(i=0;i<sz;i++)
        {
            int from=prerequisites[i][1];
            int to=prerequisites[i][0];
            indegree[to]++;
            graph[from].push_back(to);
        }
        queue<int>q;
        for(i=0;i<numCourses;i++)
        {
            if(indegree[i]==0)
                q.push(i);
        }
        while(!q.empty())
        {
            fron=q.front();
            q.pop();
            con++;
            len=graph[fron].size();
            for(i=0;i<len;i++)
            {
                indegree[graph[fron][i]]--;
                if(indegree[graph[fron][i]]==0)
                    q.push(graph[fron][i]);
            }
        }
        return (con==numCourses);
    }
};