updating DIRECTORY.md

Author: cclauss

DIRECTORY.md

@@ -241,6 +241,7 @@
     * [Kth Largest Element](data_structures/arrays/kth_largest_element.py)
     * [Median Two Array](data_structures/arrays/median_two_array.py)
     * [Monotonic Array](data_structures/arrays/monotonic_array.py)
+    * [Next Greater Element](data_structures/arrays/next_greater_element.py)
     * [Pairs With Given Sum](data_structures/arrays/pairs_with_given_sum.py)
     * [Permutations](data_structures/arrays/permutations.py)
     * [Prefix Sum](data_structures/arrays/prefix_sum.py)
@@ -986,6 +987,7 @@
   * [Doppler Frequency](physics/doppler_frequency.py)
   * [Escape Velocity](physics/escape_velocity.py)
   * [Grahams Law](physics/grahams_law.py)
+  * [Hamiltonian](physics/hamiltonian.py)
   * [Horizontal Projectile Motion](physics/horizontal_projectile_motion.py)
   * [Hubble Parameter](physics/hubble_parameter.py)
   * [Ideal Gas Law](physics/ideal_gas_law.py)