updating DIRECTORY.md

Author: cclauss

DIRECTORY.md

@@ -345,12 +345,12 @@
     * [Dijkstras Two Stack Algorithm](data_structures/stacks/dijkstras_two_stack_algorithm.py)
     * [Infix To Postfix Conversion](data_structures/stacks/infix_to_postfix_conversion.py)
     * [Infix To Prefix Conversion](data_structures/stacks/infix_to_prefix_conversion.py)
-    * [Postfix to Prefix Conversion](data_structures/stacks/postfix_to_prefix_conversion.py)
     * [Kth Next Greater Element](data_structures/stacks/kth_next_greater_element.py)
     * [Largest Rectangle Histogram](data_structures/stacks/largest_rectangle_histogram.py)
     * [Lexicographical Numbers](data_structures/stacks/lexicographical_numbers.py)
     * [Next Greater Element](data_structures/stacks/next_greater_element.py)
     * [Postfix Evaluation](data_structures/stacks/postfix_evaluation.py)
+    * [Postfix To Prefix Conversion](data_structures/stacks/postfix_to_prefix_conversion.py)
     * [Prefix Evaluation](data_structures/stacks/prefix_evaluation.py)
     * [Stack](data_structures/stacks/stack.py)
     * [Stack Using Two Queues](data_structures/stacks/stack_using_two_queues.py)
@@ -987,6 +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)