207.py

# Course Schedule

class Solution:
    def canFinish(self, numCourses: int, prerequisites: List[List[int]]) -> bool:
        adj=[[] for _ in range(numCourses)]
        for course, pre in prerequisites:
            adj[pre].append(course)
        
        vis=[False]*numCourses
        path=[False]*numCourses

        def dfs(node):
            vis[node] = path[node]=True

            for next_node in adj[node]:
                if not vis[next_node]:
                    if dfs(next_node): return True
                elif path[next_node]: return True
            
            path[node]=False
            return False
        
        for i in range(numCourses):
            if not vis[i]:
                if dfs(i): return False
        
        return True