Add default arguments for Project Euler problem 6 (TheAlgorithms#2957)

- Add default arguments to solution function
- Add link to Project Euler problem 6
- Add doctest for testing `solution()`
- Removed test_solutions.py as it is redundant

Author: dhruvmanila

Diff for: project_euler/problem_06/sol1.py

@@ -1,5 +1,5 @@
 """
-Problem:
+Problem 6: https://projecteuler.net/problem=6
 
 The sum of the squares of the first ten natural numbers is,
             1^2 + 2^2 + ... + 10^2 = 385
@@ -15,7 +15,7 @@
 """
 
 
-def solution(n: int) -> int:
+def solution(n: int = 100) -> int:
     """Returns the difference between the sum of the squares of the first n
     natural numbers and the square of the sum.
 
@@ -27,6 +27,8 @@ def solution(n: int) -> int:
     41230
     >>> solution(50)
     1582700
+    >>> solution()
+    25164150
     """
     sum_of_squares = 0
     sum_of_ints = 0

Diff for: project_euler/problem_06/sol2.py

@@ -1,5 +1,5 @@
 """
-Problem:
+Problem 6: https://projecteuler.net/problem=6
 
 The sum of the squares of the first ten natural numbers is,
             1^2 + 2^2 + ... + 10^2 = 385
@@ -15,7 +15,7 @@
 """
 
 
-def solution(n: int) -> int:
+def solution(n: int = 100) -> int:
     """Returns the difference between the sum of the squares of the first n
     natural numbers and the square of the sum.
 
@@ -27,6 +27,8 @@ def solution(n: int) -> int:
     41230
     >>> solution(50)
     1582700
+    >>> solution()
+    25164150
     """
     sum_cubes = (n * (n + 1) // 2) ** 2
     sum_squares = n * (n + 1) * (2 * n + 1) // 6

Diff for: project_euler/problem_06/sol3.py

@@ -1,5 +1,5 @@
 """
-Problem:
+Problem 6: https://projecteuler.net/problem=6
 
 The sum of the squares of the first ten natural numbers is,
             1^2 + 2^2 + ... + 10^2 = 385
@@ -16,7 +16,7 @@
 import math
 
 
-def solution(n: int) -> int:
+def solution(n: int = 100) -> int:
     """Returns the difference between the sum of the squares of the first n
     natural numbers and the square of the sum.
 
@@ -28,6 +28,8 @@ def solution(n: int) -> int:
     41230
     >>> solution(50)
     1582700
+    >>> solution()
+    25164150
     """
     sum_of_squares = sum([i * i for i in range(1, n + 1)])
     square_of_sum = int(math.pow(sum(range(1, n + 1)), 2))

Diff for: project_euler/problem_06/sol4.py

@@ -1,5 +1,5 @@
 """
-Problem:
+Problem 6: https://projecteuler.net/problem=6
 
 The sum of the squares of the first ten natural numbers is,
             1^2 + 2^2 + ... + 10^2 = 385
@@ -15,7 +15,7 @@
 """
 
 
-def solution(n: int) -> int:
+def solution(n: int = 100) -> int:
     """Returns the difference between the sum of the squares of the first n
     natural numbers and the square of the sum.
 
@@ -27,7 +27,7 @@ def solution(n: int) -> int:
     41230
     >>> solution(50)
     1582700
-    >>> solution(100)
+    >>> solution()
     25164150
     """
     sum_of_squares = n * (n + 1) * (2 * n + 1) / 6