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

C# 207-Course-Schedule.cs

Author: Ahmad-A0

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; 
+        }
+}