refactor: use Package.swift to define executable task

codes/swift/utils/PrintUtil.swift

@@ -0,0 +1,61 @@
+/*
+ * File: PrintUtil.swift
+ * Created Time: 2023-01-02
+ * Author: nuomi1 (nuomi1@qq.com)
+ */
+
+public enum PrintUtil {
+    private class Trunk {
+        var prev: Trunk?
+        var str: String
+
+        init(prev: Trunk?, str: String) {
+            self.prev = prev
+            self.str = str
+        }
+    }
+
+    public static func printTree(root: TreeNode?) {
+        printTree(root: root, prev: nil, isLeft: false)
+    }
+
+    private static func printTree(root: TreeNode?, prev: Trunk?, isLeft: Bool) {
+        if root == nil {
+            return
+        }
+
+        var prevStr = "    "
+        let trunk = Trunk(prev: prev, str: prevStr)
+
+        printTree(root: root?.right, prev: trunk, isLeft: true)
+
+        if prev == nil {
+            trunk.str = "———"
+        } else if isLeft {
+            trunk.str = "/———"
+            prevStr = "   |"
+        } else {
+            trunk.str = "\\———"
+            prev?.str = prevStr
+        }
+
+        showTrunks(p: trunk)
+        print(" \(root!.val)")
+
+        if prev != nil {
+            prev?.str = prevStr
+        }
+        trunk.str = "   |"
+
+        printTree(root: root?.left, prev: trunk, isLeft: false)
+    }
+
+    private static func showTrunks(p: Trunk?) {
+        if p == nil {
+            return
+        }
+
+        showTrunks(p: p?.prev)
+        print(p!.str, terminator: "")
+    }
+}