refactor: extract Vertex and use Array<Vertex> (#374)

* refactor: extract Vertex and use Array<Vertex>

* docs: add chapter to Package.swift

* Update graph_adjacency_list.swift

---------

Co-authored-by: Yudong Jin <krahets@163.com>

codes/swift/utils/Vertex.swift

@@ -0,0 +1,40 @@
+/**
+ * File: Vertex.swift
+ * Created Time: 2023-02-19
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+/* 顶点类 */
+public class Vertex: Hashable {
+    public var val: Int
+
+    public init(val: Int) {
+        self.val = val
+    }
+
+    public static func == (lhs: Vertex, rhs: Vertex) -> Bool {
+        lhs.val == rhs.val
+    }
+
+    public func hash(into hasher: inout Hasher) {
+        hasher.combine(val)
+    }
+
+    /* 输入值列表 vals ，返回顶点列表 vets */
+    public static func valsToVets(_ vals: [Int]) -> [Vertex] {
+        var vets: [Vertex] = []
+        for val in vals {
+            vets.append(Vertex(val: val))
+        }
+        return vets
+    }
+
+    /* 输入顶点列表 vets ，返回值列表 vals */
+    public static func vetsToVals(_ vets: [Vertex]) -> [Int] {
+        var vals: [Int] = []
+        for vet in vets {
+            vals.append(vet.val)
+        }
+        return vals
+    }
+}