Course Schedule II

Problem page:https://leetcode.com/problems/course-schedule-ii

Solution

class Solution:
    def findOrder(self, numCourses: int, prerequisites: List[List[int]]) -> List[int]:
        adj = [[] for _ in range(numCourses)]
        indegree = [0] * numCourses
        ans = []

        for pair in prerequisites:
            course = pair[0]
            prerequisite = pair[1]
            adj[prerequisite].append(course)
            indegree[course] += 1

        queue = deque()
        for i in range(numCourses):
            if indegree[i] == 0:
                queue.append(i)

        while queue:
            current = queue.popleft()
            ans.append(current)

            for next_course in adj[current]:
                indegree[next_course] -= 1
                if indegree[next_course] == 0:
                    queue.append(next_course)

        if len(ans) < numCourses:
            return []
        return ans

Complexity

• time: O(V + E)
• space: O(V + E)