Add code for chapter 3 and 4 in ts (#103)

03_recursion/ts/03_factorial.ts

@@ -0,0 +1,9 @@
+function fact(x: number): number {
+    if (x === 1) {
+        return x;
+    }
+
+    return x * fact(x - 1);
+}
+
+console.log(fact(5));