feat: add dart code for chapter_graph (#498)

codes/dart/utils/print_util.dart

@@ -16,6 +16,14 @@ class Trunk {
   Trunk(this.prev, this.str);
 }
 
+void printMatrix(List<List<int>> matrix) {
+  print("[");
+  for (List<int> row in matrix) {
+    print("  $row,");
+  }
+  print("]");
+}
+
 void printLinkedList(ListNode? head) {
   List<String> list = [];
 

codes/dart/utils/vertex.dart

@@ -0,0 +1,29 @@
+/**
+ * File: Vertex.dart
+ * Created Time: 2023-05-15
+ * Author: liuyuxin (gvenusleo@gmail.com)
+ */
+
+/* 顶点类 */
+class Vertex {
+  int val;
+  Vertex(this.val);
+
+  /* 输入值列表 vals ，返回顶点列表 vets */
+  static List<Vertex> valsToVets(List<int> vals) {
+    List<Vertex> vets = [];
+    for (int i in vals) {
+      vets.add(Vertex(i));
+    }
+    return vets;
+  }
+
+  /* 输入顶点列表 vets ，返回值列表 vals */
+  static List<int> vetsToVals(List<Vertex> vets) {
+    List<int> vals = [];
+    for (Vertex vet in vets) {
+      vals.add(vet.val);
+    }
+    return vals;
+  }
+}