Course Schedule II

1from collections import deque
2
3def findOrder(numCourses: int, prerequisites: List[List[int]]) -> List[int]:
4    graph = [[] for _ in range(numCourses)]
5    indeg = [0] * numCourses
6    for a, b in prerequisites:
7        graph[b].append(a)
8        indeg[a] += 1
9        
10    q = deque([i for i in range(numCourses) if indeg[i] == 0])
11    order = []
12    
13    while q:
14        cur = q.popleft()
15        order.append(cur)
16        for nxt in graph[cur]:
17            indeg[nxt] -= 1
18            if indeg[nxt] == 0:
19                q.append(nxt)
20    
21    return order if len(order) == numCourses else []