Add code for chapter 5 in ts (#104)

05_hash_tables/ts/01_price_of_groceries.ts

@@ -0,0 +1,11 @@
+interface HashTable<T> {
+    [key: string]: T;
+}
+
+const book: HashTable<number> = {};
+
+book['apple'] = 0.67;
+book['milk'] = 1.49;
+book['avocado'] = 1.49;
+
+console.log(book); // { apple: 0.67, milk: 1.49, avocado: 1.49 }

05_hash_tables/ts/02_check_voter.ts

@@ -0,0 +1,18 @@
+interface HashTable<T> {
+    [key: string]: T;
+}
+
+const voted: HashTable<boolean> = {};
+
+function check_voter(name: string): void {
+    if (voted[name]) {
+        console.log('kick them out!');
+    } else {
+        voted[name] = true;
+        console.log('let them vote!');
+    }
+}
+
+check_voter("tom"); // let them vote!
+check_voter("mike"); // let them vote!
+check_voter("mike"); // kick them out!