updating DIRECTORY.md

Author: github-actions

Diff for: DIRECTORY.md

@@ -51,6 +51,7 @@
   * [Index Of Rightmost Set Bit](bit_manipulation/index_of_rightmost_set_bit.py)
   * [Is Even](bit_manipulation/is_even.py)
   * [Is Power Of Two](bit_manipulation/is_power_of_two.py)
+  * [Missing Number](bit_manipulation/missing_number.py)
   * [Numbers Different Signs](bit_manipulation/numbers_different_signs.py)
   * [Reverse Bits](bit_manipulation/reverse_bits.py)
   * [Single Bit Manipulation Operations](bit_manipulation/single_bit_manipulation_operations.py)
@@ -676,6 +677,7 @@
   * [Sylvester Sequence](maths/sylvester_sequence.py)
   * [Tanh](maths/tanh.py)
   * [Test Prime Check](maths/test_prime_check.py)
+  * [Three Sum](maths/three_sum.py)
   * [Trapezoidal Rule](maths/trapezoidal_rule.py)
   * [Triplet Sum](maths/triplet_sum.py)
   * [Twin Prime](maths/twin_prime.py)