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_11/sol1.py

@@ -1,6 +1,6 @@
-from __future__ import print_function
-'''
-What is the greatest product of four adjacent numbers (horizontally, vertically, or diagonally) in this 20x20 array?
+"""
+What is the greatest product of four adjacent numbers (horizontally,
+vertically, or diagonally) in this 20x20 array?
 
 08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08
 49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00
@@ -22,47 +22,78 @@ What is the greatest product of four adjacent numbers (horizontally, vertically,
 20 69 36 41 72 30 23 88 34 62 99 69 82 67 59 85 74 04 36 16
 20 73 35 29 78 31 90 01 74 31 49 71 48 86 81 16 23 57 05 54
 01 70 54 71 83 51 54 69 16 92 33 48 61 43 52 01 89 19 67 48
-'''
+"""
+
+from __future__ import print_function
+import os
 
 try:
-	xrange			#Python 2
+    xrange  # Python 2
 except NameError:
-	xrange = range	#Python 2
+    xrange = range  # Python 2
+
 
 def largest_product(grid):
-	nColumns = len(grid[0])
-	nRows = len(grid)
+    nColumns = len(grid[0])
+    nRows = len(grid)
 
-	largest = 0
-	lrDiagProduct = 0
-	rlDiagProduct = 0
+    largest = 0
+    lrDiagProduct = 0
+    rlDiagProduct = 0
 
-	#Check vertically, horizontally, diagonally at the same time (only works for nxn grid)
-	for i in xrange(nColumns):
-		for j in xrange(nRows-3):
-			vertProduct = grid[j][i]*grid[j+1][i]*grid[j+2][i]*grid[j+3][i]
-			horzProduct = grid[i][j]*grid[i][j+1]*grid[i][j+2]*grid[i][j+3]
+    # Check vertically, horizontally, diagonally at the same time (only works
+    # for nxn grid)
+    for i in xrange(nColumns):
+        for j in xrange(nRows - 3):
+            vertProduct = (
+                grid[j][i] * grid[j + 1][i] * grid[j + 2][i] * grid[j + 3][i]
+            )
+            horzProduct = (
+                grid[i][j] * grid[i][j + 1] * grid[i][j + 2] * grid[i][j + 3]
+            )
 
-			#Left-to-right diagonal (\) product
-			if (i < nColumns-3):
-				lrDiagProduct = grid[i][j]*grid[i+1][j+1]*grid[i+2][j+2]*grid[i+3][j+3]
+            # Left-to-right diagonal (\) product
+            if i < nColumns - 3:
+                lrDiagProduct = (
+                    grid[i][j]
+                    * grid[i + 1][j + 1]
+                    * grid[i + 2][j + 2]
+                    * grid[i + 3][j + 3]
+                )
 
-			#Right-to-left diagonal(/) product
-			if (i > 2):
-				rlDiagProduct = grid[i][j]*grid[i-1][j+1]*grid[i-2][j+2]*grid[i-3][j+3]
+            # Right-to-left diagonal(/) product
+            if i > 2:
+                rlDiagProduct = (
+                    grid[i][j]
+                    * grid[i - 1][j + 1]
+                    * grid[i - 2][j + 2]
+                    * grid[i - 3][j + 3]
+                )
 
-			maxProduct = max(vertProduct, horzProduct, lrDiagProduct, rlDiagProduct)
-			if maxProduct > largest:
-				largest = maxProduct
+            maxProduct = max(
+                vertProduct, horzProduct, lrDiagProduct, rlDiagProduct
+            )
+            if maxProduct > largest:
+                largest = maxProduct
 
-	return largest
+    return largest
 
-if __name__ == '__main__':
-	grid = []
-	with open('grid.txt') as file:
-		for line in file:
-			grid.append(line.strip('\n').split(' '))
 
-	grid = [[int(i) for i in grid[j]] for j in xrange(len(grid))]
+def solution():
+    """Returns the sum of all the multiples of 3 or 5 below n.
+    
+    >>> solution()
+    70600674
+    """
+    grid = []
+    with open(os.path.dirname(__file__) + "/grid.txt") as file:
+        for line in file:
+            grid.append(line.strip("\n").split(" "))
 
-	print(largest_product(grid))
+    grid = [[int(i) for i in grid[j]] for j in xrange(len(grid))]
+
+    return largest_product(grid)
+
+
+if __name__ == "__main__":
+    print(solution())