Leetcode 207: Course Schedule

Problem Statement: https://leetcode.com/problems/course-schedule/

Video Explanation: https://youtu.be/s_S2VDqBkc0

class Solution:
    def canFinish(self, numCourses: int, prerequisites: List[List[int]]) -> bool:
        
        adjlist = defaultdict(list)
        degree = { i:0 for i in range(numCourses)}
for course, prereq in prerequisites:
            adjlist[prereq].append(course)
            degree[course] = degree[course]+1
        
#         find all the nodes with in degree = 0
        q = [i for i in degree.keys() if degree[i] == 0]
#     We have a starting point
        finished = 0
        while q:
            top = q.pop()
            finished+=1
            for adj in adjlist[top]:
#                 all neighbours delete 1 from degree
                degree[adj] = degree[adj]-1
#     if no more in degree for this item pop it off and add to the queue
                if degree[adj] == 0:
                    q.append(adj)
        return finished == numCourses