Added Dart examples for chapter 3 to chapter 9 (#265)

* fix: corrected method return value following Dart's newest linter version

* feat: added Dart recursion examples for chapter 3

* feat: added quicksort example in Dart for chapter 4

* feat: added examples in Dart for the chapter 5

* feat: added Dart example for chapter 6 bfs

* feat: added djikstra example in Dart for chapter 7

* feat: added example of set covering in Dart for chapter 8

* feat: added examples for dynamic programming in dart for chapter 9

08_greedy_algorithms/dart/01_set_covering.dart

@@ -0,0 +1,52 @@
+void main(List<String> args) {
+  final fruits = {'avocado', 'tomato', 'banana'};
+  final vegetables = {'beet', 'carrot', 'tomato'};
+
+  print(fruits.union(vegetables));
+  print(fruits.intersection(vegetables));
+  print(fruits.difference(vegetables));
+  print(vegetables.difference(fruits));
+
+  final coverStates = {
+    'mt',
+    'wa',
+    'or',
+    'id',
+    'nv',
+    'ut',
+    'ca',
+    'az',
+  };
+
+  final stations = <String, Set<String>>{}..addAll(
+      {
+        'kone': {'id', 'nv', 'uy'},
+        'ktwo': {'wa', 'id', 'mt'},
+        'kthree': {'or', 'nv', 'ca'},
+        'kfour': {'nv', 'ut'},
+        'kfive': {'ca', 'az'},
+      },
+    );
+
+  final finalStations = stationSet(coverStates, stations);
+  print(finalStations);
+}
+
+Set<String> stationSet(
+    Set<String> coverStates, Map<String, Set<String>> stations) {
+  final finalStations = <String>{};
+  while (coverStates.isNotEmpty) {
+    String? bestStation;
+    Set<String> coveredStates = {};
+    for (String station in stations.keys) {
+      final covered = coverStates.intersection(stations[station] ?? {});
+      if (covered.length > coveredStates.length) {
+        bestStation = station;
+        coveredStates = covered;
+      }
+    }
+    coverStates.removeWhere((element) => coveredStates.contains(element));
+    finalStations.add(bestStation!);
+  }
+  return finalStations;
+}