Merge pull request neetcode-gh#1030 from agnihotriketan/patch-9

C# 207-Course-Schedule.cs

csharp/207-Course-Schedule.cs

@@ -0,0 +1,50 @@
+public class Solution {
+ public bool CanFinish(int numCourses, int[][] prerequisites)
+ {
+
+ IDictionary<int, List<int>> preMap = new Dictionary<int, List<int>>();
+ HashSet<int> visited = new HashSet<int>();
+ for (int i = 0; i < numCourses; i++)
+ {
+ preMap.Add(i, new List<int>());
+ }
+
+ foreach (int[] course in prerequisites)
+ {
+ int courseToTake = course[0];
+ int courseDependOn = course[1];
+ preMap[courseToTake].Add(courseDependOn);
+ }
+
+ foreach (int c in Enumerable.Range(0, numCourses))
+ {
+ if (!DfsGraph(preMap, visited, c))
+ {
+ return false;
+ }
+ }
+ return true; 
+ }
+ public bool DfsGraph(IDictionary<int, List<int>> preMap, HashSet<int> visited, int crs)
+ {
+ if (visited.Contains(crs))
+ {
+ return false;
+ }
+ if (preMap[crs] == new List<int>())
+ {
+ return true;
+ }
+ visited.Add(crs);
+ foreach (var pre in preMap[crs])
+ {
+ if (!DfsGraph(preMap, visited, pre))
+ {
+ return false;
+ }
+ }
+ visited.Remove(crs);
+ preMap[crs] = new List<int>();
+ return true; 
+ }
+}