Course Schedule (Cycle Detection in Directed Graph)

Problem: Course Schedule (Can You Finish All Courses?) You are given an integer numCourses (course labels 0 ... numCourses-1) and an array prerequisites, where each element is [a, b] meaning to take course a, you must first take course b. Return true if you can finish all courses. If the prerequisite graph contains a directed cycle, return false; otherwise return true. Input Integer numCourses 2D array prerequisites, each element is a length-2 array [a, b] Output Boolean indicating whether all courses can be finished Constraints / Scale 1 <= numCourses <= 2 * 10^5 0 <= prerequisites.length <= 2 * 10^5 0 <= a, b < numCourses a != b Target time complexity: O(V + E). Examples numCourses = 2, prerequisites = [[1,0]] → true numCourses = 2, prerequisites = [[1,0],[0,1]] → false numCourses = 4, prerequisites = [[1,0],[2,0],[3,1],[3,2]] → true numCourses = 3, prerequisites = [[0,1],[1,2],[2,0]] → false numCourses = 5, prerequisites = [] → true Example Input 2 1 1 0 Output true