feat: add cs solution to lc problem: No.815 (#1957)

Author: dev-mauli

solution/0800-0899/0815.Bus Routes/README.md

@@ -281,6 +281,65 @@ func numBusesToDestination(routes [][]int, source int, target int) int {
 }
 ```
 
+### **C#**
+
+```cs
+public class Solution {
+    public int NumBusesToDestination(int[][] routes, int source, int target) {
+        if (source == target) {
+            return 0;
+        }
+
+        Dictionary<int, HashSet<int>> stopToRoutes = new Dictionary<int, HashSet<int>>();
+        List<HashSet<int>> routeToStops = new List<HashSet<int>>();
+
+        for (int i = 0; i < routes.Length; i++) {
+            routeToStops.Add(new HashSet<int>());
+            foreach (int stop in routes[i]) {
+                routeToStops[i].Add(stop);
+                if (!stopToRoutes.ContainsKey(stop)) {
+                    stopToRoutes[stop] = new HashSet<int>();
+                }
+                stopToRoutes[stop].Add(i);
+            }
+        }
+
+        Queue<int> queue = new Queue<int>();
+        HashSet<int> visited = new HashSet<int>();
+        int ans = 0;
+
+        foreach (int routeId in stopToRoutes[source]) {
+            queue.Enqueue(routeId);
+            visited.Add(routeId);
+        }
+
+        while (queue.Count > 0) {
+            int count = queue.Count;
+            ans++;
+
+            for (int i = 0; i < count; i++) {
+                int routeId = queue.Dequeue();
+
+                foreach (int stop in routeToStops[routeId]) {
+                    if (stop == target) {
+                        return ans;
+                    }
+
+                    foreach (int nextRoute in stopToRoutes[stop]) {
+                        if (!visited.Contains(nextRoute)) {
+                            visited.Add(nextRoute);
+                            queue.Enqueue(nextRoute);
+                        }
+                    }
+                }
+            }
+        }
+
+        return -1;
+    }
+}
+```
+
 ### **...**
 
 ```

solution/0800-0899/0815.Bus Routes/README_EN.md

@@ -256,6 +256,65 @@ func numBusesToDestination(routes [][]int, source int, target int) int {
 }
 ```
 
+### **C#**
+
+```cs
+public class Solution {
+    public int NumBusesToDestination(int[][] routes, int source, int target) {
+        if (source == target) {
+            return 0;
+        }
+
+        Dictionary<int, HashSet<int>> stopToRoutes = new Dictionary<int, HashSet<int>>();
+        List<HashSet<int>> routeToStops = new List<HashSet<int>>();
+
+        for (int i = 0; i < routes.Length; i++) {
+            routeToStops.Add(new HashSet<int>());
+            foreach (int stop in routes[i]) {
+                routeToStops[i].Add(stop);
+                if (!stopToRoutes.ContainsKey(stop)) {
+                    stopToRoutes[stop] = new HashSet<int>();
+                }
+                stopToRoutes[stop].Add(i);
+            }
+        }
+
+        Queue<int> queue = new Queue<int>();
+        HashSet<int> visited = new HashSet<int>();
+        int ans = 0;
+
+        foreach (int routeId in stopToRoutes[source]) {
+            queue.Enqueue(routeId);
+            visited.Add(routeId);
+        }
+
+        while (queue.Count > 0) {
+            int count = queue.Count;
+            ans++;
+
+            for (int i = 0; i < count; i++) {
+                int routeId = queue.Dequeue();
+
+                foreach (int stop in routeToStops[routeId]) {
+                    if (stop == target) {
+                        return ans;
+                    }
+
+                    foreach (int nextRoute in stopToRoutes[stop]) {
+                        if (!visited.Contains(nextRoute)) {
+                            visited.Add(nextRoute);
+                            queue.Enqueue(nextRoute);
+                        }
+                    }
+                }
+            }
+        }
+
+        return -1;
+    }
+}
+```
+
 ### **...**
 
 ```

solution/0800-0899/0815.Bus Routes/Solution.cs

@@ -0,0 +1,54 @@
+public class Solution {
+    public int NumBusesToDestination(int[][] routes, int source, int target) {
+        if (source == target) {
+            return 0;
+        }
+        
+        Dictionary<int, HashSet<int>> stopToRoutes = new Dictionary<int, HashSet<int>>();
+        List<HashSet<int>> routeToStops = new List<HashSet<int>>();
+        
+        for (int i = 0; i < routes.Length; i++) {
+            routeToStops.Add(new HashSet<int>());
+            foreach (int stop in routes[i]) {
+                routeToStops[i].Add(stop);
+                if (!stopToRoutes.ContainsKey(stop)) {
+                    stopToRoutes[stop] = new HashSet<int>();
+                }
+                stopToRoutes[stop].Add(i);
+            }
+        }
+        
+        Queue<int> queue = new Queue<int>();
+        HashSet<int> visited = new HashSet<int>();
+        int ans = 0;
+
+        foreach (int routeId in stopToRoutes[source]) {
+            queue.Enqueue(routeId);
+            visited.Add(routeId);
+        }
+
+        while (queue.Count > 0) {
+            int count = queue.Count;
+            ans++;
+
+            for (int i = 0; i < count; i++) {
+                int routeId = queue.Dequeue();
+
+                foreach (int stop in routeToStops[routeId]) {
+                    if (stop == target) {
+                        return ans;
+                    }
+
+                    foreach (int nextRoute in stopToRoutes[stop]) {
+                        if (!visited.Contains(nextRoute)) {
+                            visited.Add(nextRoute);
+                            queue.Enqueue(nextRoute);
+                        }
+                    }
+                }
+            }
+        }
+
+        return -1;
+    }
+}