Commented doctests that were causing slowness at Travis. (#1039)

* Added doctest and more explanation about Dijkstra execution.

* tests were not passing with python2 due to missing __init__.py file at number_theory folder

* Removed the dot at the beginning of the imported modules names because 'python3 -m doctest -v data_structures/hashing/*.py' and 'python3 -m doctest -v data_structures/stacks/*.py' were failing not finding hash_table.py and stack.py modules.

* Moved global code to main scope and added doctest for project euler problems 1 to 14.

* Added test case for negative input.

* Changed N variable to do not use end of line scape because in case there is a space after it the script will break making it much more error prone.

* Added problems description and doctests to the ones that were missing. Limited line length to 79 and executed python black over all scripts.

* Changed the way files are loaded to support pytest call.

* Added __init__.py to problems to make them modules and allow pytest execution.

* Added project_euler folder to test units execution

* Changed 'os.path.split(os.path.realpath(__file__))' to 'os.path.dirname()'

* Added Burrows-Wheeler transform algorithm.

* Added changes suggested by cclauss

* Fixes for issue 'Fix the LGTM issues #1024'.

* Added doctest for different parameter types and negative values.

* Fixed doctest issue added at last commit.

* Commented doctest that were causing slowness at Travis.

* Added comment with the reason for some doctest commented.

* pytest --ignore

project_euler/problem_09/sol1.py

@@ -18,8 +18,9 @@ def solution():
      2. a**2 + b**2 = c**2
      3. a + b + c = 1000
     
-    >>> solution()
-    31875000
+    # The code below has been commented due to slow execution affecting Travis.
+    # >>> solution()
+    # 31875000
     """
     for a in range(300):
         for b in range(400):

project_euler/problem_09/sol3.py

@@ -21,8 +21,8 @@ def solution():
      1. a**2 + b**2 = c**2
      2. a + b + c = 1000
 
-    >>> solution()
-    31875000
+    #>>> solution()
+    #31875000
     """
     return [
         a * b * c

project_euler/problem_10/sol1.py

@@ -42,8 +42,9 @@ def sum_of_primes(n):
 def solution(n):
     """Returns the sum of all the primes below n.
     
-    >>> solution(2000000)
-    142913828922
+    # The code below has been commented due to slow execution affecting Travis.
+    # >>> solution(2000000)
+    # 142913828922
     >>> solution(1000)
     76127
     >>> solution(5000)

project_euler/problem_10/sol2.py

@@ -31,8 +31,9 @@ def prime_generator():
 def solution(n):
     """Returns the sum of all the primes below n.
     
-    >>> solution(2000000)
-    142913828922
+    # The code below has been commented due to slow execution affecting Travis.
+    # >>> solution(2000000)
+    # 142913828922
     >>> solution(1000)
     76127
     >>> solution(5000)

project_euler/problem_12/sol1.py

@@ -45,8 +45,9 @@ def solution():
     """Returns the value of the first triangle number to have over five hundred
     divisors.
     
-    >>> solution()
-    76576500
+    # The code below has been commented due to slow execution affecting Travis.
+    # >>> solution()
+    # 76576500
     """
     tNum = 1
     i = 1

project_euler/problem_12/sol2.py

@@ -39,8 +39,9 @@ def solution():
     """Returns the value of the first triangle number to have over five hundred
     divisors.
     
-    >>> solution()
-    76576500
+    # The code below has been commented due to slow execution affecting Travis.
+    # >>> solution()
+    # 76576500
     """
     return next(
         i for i in triangle_number_generator() if count_divisors(i) > 500

project_euler/problem_14/sol1.py

@@ -30,8 +30,9 @@ def solution(n):
     n → n/2 (n is even)
     n → 3n + 1 (n is odd)
  
-    >>> solution(1000000)
-    {'counter': 525, 'largest_number': 837799}
+    # The code below has been commented due to slow execution affecting Travis.
+    # >>> solution(1000000)
+    # {'counter': 525, 'largest_number': 837799}
     >>> solution(200)
     {'counter': 125, 'largest_number': 171}
     >>> solution(5000)

project_euler/problem_14/sol2.py

@@ -47,8 +47,9 @@ def collatz_sequence(n):
 def solution(n):
     """Returns the number under n that generates the longest Collatz sequence.
 
-    >>> solution(1000000)
-    {'counter': 525, 'largest_number': 837799}
+    # The code below has been commented due to slow execution affecting Travis.
+    # >>> solution(1000000)
+    # {'counter': 525, 'largest_number': 837799}
     >>> solution(200)
     {'counter': 125, 'largest_number': 171}
     >>> solution(5000)