updating DIRECTORY.md

Author: cclauss

DIRECTORY.md

@@ -966,6 +966,7 @@
     * [Happy Number](maths/special_numbers/happy_number.py)
     * [Harshad Numbers](maths/special_numbers/harshad_numbers.py)
     * [Hexagonal Number](maths/special_numbers/hexagonal_number.py)
+    * [Jacobsthal Number](maths/special_numbers/jacobsthal_number.py)
     * [Kaprekar Constant](maths/special_numbers/kaprekar_constant.py)
     * [Kaprekar Number](maths/special_numbers/kaprekar_number.py)
     * [Krishnamurthy Number](maths/special_numbers/krishnamurthy_number.py)
@@ -1602,6 +1603,7 @@
   * [Lower](strings/lower.py)
   * [Manacher](strings/manacher.py)
   * [Min Cost String Conversion](strings/min_cost_string_conversion.py)
+  * [Min Window Substring](strings/min_window_substring.py)
   * [Naive String Search](strings/naive_string_search.py)
   * [Ngram](strings/ngram.py)
   * [Palindrome](strings/palindrome.py)