207. Course Schedule

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class Solution:
    def canFinish(self, numCourses: int, prerequisites: List[List[int]]) -> bool:

        indeg = [0] * numCourses

        M = defaultdict(list)


        for v1 , v2 in prerequisites:
            M[v2].append(v1)
            indeg[v1] += 1

        

        q = deque([i for i in range(len(indeg)) if indeg[i] == 0])

        visited = set()

        while q:
            node = q.popleft()

            

            if node in visited:
                continue

            visited.add(node)

            for vv in M[node]:
                indeg[vv] -= 1

                if indeg[vv] == 0:
                    q.append(vv)


        return len(visited) == numCourses