Create 1466-Reorder-Routes-to-Make- All-Paths-Lead-to-the-City-Zero.cs

Author: agnihotriketan

Diff for: csharp/1466-Reorder-Routes-to-Make- All-Paths-Lead-to-the-City-Zero.cs

@@ -0,0 +1,47 @@
+public class Solution {
+  public int MinReorder(int n, int[][] connections)
+        {
+            if (connections == null || connections?.Length < 2) return 0;
+
+            Dictionary<int, HashSet<int>> paths = new Dictionary<int, HashSet<int>>();
+            List<int>[] graph = new List<int>[n];
+            foreach (var connection in connections)
+            {
+                if (!paths.ContainsKey(connection[0]))
+                    paths.Add(connection[0], new HashSet<int>());
+
+                paths[connection[0]].Add(connection[1]);
+
+                if (graph[connection[0]] == null)
+                    graph[connection[0]] = new List<int>();
+                graph[connection[0]].Add(connection[1]);
+
+                if (graph[connection[1]] == null)
+                    graph[connection[1]] = new List<int>();
+                graph[connection[1]].Add(connection[0]);
+            }
+            int cnt = 0;
+            HashSet<int> visited = new HashSet<int>();
+            DFSMinReorder(graph, 0, paths, visited, ref cnt);
+            return cnt;
+        }
+
+        private void DFSMinReorder(List<int>[] graph, int u, Dictionary<int, HashSet<int>> paths, HashSet<int> visited, ref int cnt)
+        {
+            visited.Add(u);
+
+            if (graph[u] != null)
+            {
+                foreach (var v in graph[u])
+                {
+                    if (!visited.Contains(v))
+                    {
+                        if (paths.ContainsKey(u) && paths[u].Contains(v))
+                            cnt++;
+
+                        DFSMinReorder(graph, v, paths, visited, ref cnt);
+                    }
+                }
+            }
+        }
+}