题目描述：

第一次提交：

class Solution:
def findOrder(self, numCourses: int, prerequisites: List[List[int]]) -> List[int]:
indegree = [0 for _ in range(numCourses)]
adj = [[] for _ in range(numCourses)]
for cur,pre in prerequisites:
adj[pre].append(cur)
indegree[cur] += 1
res = []
queue = []
for i in range(numCourses):
if indegree[i] == 0:
queue.append(i)
while queue:
i = queue.pop(0)
res.append(i)
for j in adj[i]:
indegree[j] -= 1
if indegree[j] == 0:
queue.append(j)
return res if len(res) == numCourses else []

方法二：dfs + 栈

class Solution:
def findOrder(self, numCourses: int, prerequisites: List[List[int]]) -> List[int]:
def dfs(i, adjacency, flags):
if flags[i] == -1: return True
if flags[i] == 1: return False
flags[i] = 1
for j in adjacency[i]:
if not dfs(j, adjacency, flags): return False
flags[i] = -1
res.append(i)
return True
res = []
adjacency = [[] for _ in range(numCourses)]
flags = [0 for _ in range(numCourses)]
for cur, pre in prerequisites:
adjacency[pre].append(cur)
for i in range(numCourses):
if not dfs(i, adjacency, flags): return []
return res[::-1]