#210

Course Schedule II

medium· Graphsruns: 0

There are numCourses courses labeled 0 to numCourses - 1. You are given an array prerequisites where prerequisites[i] = [a, b] indicates that you must take course b before course a. Return the order of courses you should take to finish all of them. If there are multiple valid answers, return any. If it is impossible to finish all courses, return an empty array.

wpm 0acc 100%time 0:000 / 846

class Solution:
    def findOrder(
        self, numCourses: int, prerequisites: list[list[int]]
    ) -> list[int]:
        graph = {i: [] for i in range(numCourses)}
        for course, pre in prerequisites:
            graph[course].append(pre)
        visit = set()
        cycle = set()
        order = []

        def dfs(course: int) -> bool:
            if course in cycle:
                return False
            if course in visit:
                return True
            cycle.add(course)
            for pre in graph[course]:
                if not dfs(pre):
                    return False
            cycle.remove(course)
            visit.add(course)
            order.append(course)
            return True

        for course in range(numCourses):
            if not dfs(course):
                return []
        return order

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