Added doctest and more explanation about Dijkstra execution. (#1014)

* 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()'

project_euler/problem_76/sol1.py

@@ -1,5 +1,4 @@
-from __future__ import print_function
-'''
+"""
 Counting Summations
 Problem 76
 
@@ -12,24 +11,50 @@ It is possible to write five as a sum in exactly six different ways:
 2 + 1 + 1 + 1
 1 + 1 + 1 + 1 + 1
 
-How many different ways can one hundred be written as a sum of at least two positive integers?
-'''
+How many different ways can one hundred be written as a sum of at least two
+positive integers?
+"""
+from __future__ import print_function
+
 try:
-	xrange		#Python 2
+    xrange  # Python 2
 except NameError:
-	xrange = range	#Python 3
+    xrange = range  # Python 3
+
 
 def partition(m):
-	memo = [[0 for _ in xrange(m)] for _ in xrange(m+1)]
-	for i in xrange(m+1):
-		memo[i][0] = 1
+    """Returns the number of different ways one hundred can be written as a sum
+    of at least two positive integers.
 
-	for n in xrange(m+1):
-		for k in xrange(1, m):
-			memo[n][k] += memo[n][k-1]
-			if n > k:
-				memo[n][k] += memo[n-k-1][k]
+    >>> partition(100)
+    190569291
+    >>> partition(50)
+    204225
+    >>> partition(30)
+    5603
+    >>> partition(10)
+    41
+    >>> partition(5)
+    6
+    >>> partition(3)
+    2
+    >>> partition(2)
+    1
+    >>> partition(1)
+    0
+    """
+    memo = [[0 for _ in xrange(m)] for _ in xrange(m + 1)]
+    for i in xrange(m + 1):
+        memo[i][0] = 1
 
-	return (memo[m][m-1] - 1)
+    for n in xrange(m + 1):
+        for k in xrange(1, m):
+            memo[n][k] += memo[n][k - 1]
+            if n > k:
+                memo[n][k] += memo[n - k - 1][k]
 
-print(partition(100))
+    return memo[m][m - 1] - 1
+
+
+if __name__ == "__main__":
+    print(partition(int(str(input()).strip())))