diff --git a/src/exercises/string/shortening-by-decode-id.ts b/src/exercises/string/shortening-by-decode-id.ts
new file mode 100644
index 0000000..1cc3997
--- /dev/null
+++ b/src/exercises/string/shortening-by-decode-id.ts
@@ -0,0 +1,15 @@
+const DICTIONARY01 = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'.split('');
+
+function decodeId(id: string) {
+  const base: number = DICTIONARY01.length;
+  let decoded: string | number = 0;
+
+  for (let i = 0; i < id.split('').length; i++) {
+    decoded = decoded * base + DICTIONARY01.indexOf(id.charAt(i));
+  }
+
+  return decoded;
+}
+
+console.log(encodeId(11231230)); // prints 'VhU2'
+console.log(decodeId('VhU2')); // prints '11231230'
diff --git a/src/exercises/string/shortening.ts b/src/exercises/string/shortening-by-encode-id.ts
similarity index 100%
rename from src/exercises/string/shortening.ts
rename to src/exercises/string/shortening-by-encode-id.ts