Course Schedule

There are a total of numCourses courses you have to take, labeled from 0 to numCourses - 1. You are given an array prerequisites 
where prerequisites[i] = [ai, bi] indicates that you must take course bi first if you want to take course ai.

For example, the pair [0, 1], indicates that to take course 0 you have to first take course 1.
Return true if you can finish all courses. Otherwise, return false.

Example 1:
Input: numCourses = 2, prerequisites = [[1,0]]
Output: true
Explanation: There are a total of 2 courses to take. 
To take course 1 you should have finished course 0. So it is possible.

Example 2:
Input: numCourses = 2, prerequisites = [[1,0],[0,1]]
Output: false
Explanation: There are a total of 2 courses to take. 
To take course 1 you should have finished course 0, and to take course 0 you should also have finished course 1. So it is impossible.
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//tc=O(numCourses+prerequsites) sc=O(numCourses+prerequisites)
class Solution {
public:
    bool canFinish(int numCourses, vector<vector<int>>& prerequisites) {
        vector<vector<int>>adjList(numCourses);
        vector<int>inDegree(numCourses,0);
        queue<int>q;
        int count=0;
        for(auto it: prerequisites){
            adjList[it[0]].push_back(it[1]);
        }

        for(int i=0;i<numCourses;i++){
            for(auto it: adjList[i]){
                inDegree[it]++;
            }
        }

        for(int i=0;i<numCourses;i++){
            if(inDegree[i]==0)
                q.push(i);
        }

        while(!q.empty()){
            int val=q.front();
            q.pop();
            count++;

            for(auto it:adjList[val]){
                inDegree[it]--;
                if(inDegree[it]==0)
                    q.push(it);
            }
        }
        return count==numCourses;
    }
};