add: x-tba/maps use as sets

x-tba/maps/05-sets/main.go

@@ -0,0 +1,49 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import "fmt"
+
+func main() {
+	// set is a data structure that contain the same element only once.
+
+	// maps can also be used as sets.
+
+	// let's create a slice of coders.
+	coders := []string{"pike", "thompson", "lovelace", "knuth"}
+
+	// let's create a map for tracking whether they are gopher or not.
+	gophers := make(map[string]bool, len(coders))
+
+	// let's mark the gophers
+	gophers["thompson"] = true
+	gophers["pike"] = true
+
+	// print the gophers
+	for _, coder := range coders {
+		// i see this a lot, especially in beginner code.
+		//
+		// you don't have to use the "comma, ok" idiom.
+		// m[k] = false for non-existing bool elements.
+		// use it to your advantage.
+		//
+		// DONT:
+		// if _, ok := gophers[coder]; ok { ... }
+		//
+		// DO:
+		// for this trick to work, you should set all the map elements to true
+		if gophers[coder] {
+			fmt.Printf("%s is a gopher.\n", coder)
+
+			// don't use else. stay at the same indentation level.
+			continue
+		}
+
+		fmt.Printf("%s is not a gopher.\n", coder)
+	}
+}

x-tba/maps/exercises/README.md

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+# IDEAS
+
+* Retrieve sorted map keys
+
+* Roman literals