private bool orderCourses(CourseGraph graph, int numCourse, int[][] prerequisites)
{
int numDependencies = prerequisites.Count();
List <CourseGraphNode> nodes = graph.nodes;
CourseGraphNode[] courses = new CourseGraphNode[nodes.Count];
//Cpature all courses which doesn't have any prerequisites
int endOfList = addNodesWithNoDependencies(courses, nodes, 0);
int toBeProcessed = 0;
while (toBeProcessed < courses.Length)
{
var course = courses[toBeProcessed];
//Circular dependency detected
if (course == null)
{
return(false);
}
//remove current element from dependency
List <CourseGraphNode> children = course.children;
foreach (var child in children)
{
//remove edge from removed node and child nodes
child.decrementDependencies();
}
//Add childrens that has no dependent nodes
endOfList = addNodesWithNoDependencies(courses, children, endOfList);
toBeProcessed++;
}
return(true);
}
private CourseGraph buildGraph(int[][] dependencies)
{
CourseGraph graph = new CourseGraph();
//Build dependencies of each graph indices from dependencies matrix
foreach (var dependency in dependencies)
{
var preCourse = graph.getOrCreateNode(dependency[1]);
var nextCourse = graph.getOrCreateNode(dependency[0]);
graph.addEdge(nextCourse, preCourse);
}
return(graph);
}
public bool CanFinish(int numCourses, int[][] prerequisites)
{
if (prerequisites == null || prerequisites.Count() == 0)
{
return(true);
}
//Step1: Build Graph from Vertices and Dependencies
//Here, [a, b] => b is a prerequisite of a
//To take a, you have to complete b
CourseGraph graph = buildGraph(prerequisites);
return(orderCourses(graph, numCourses, prerequisites));
}
