Fix style of the first ten solutions for Project Euler (#3242)

* Fix style of the first ten solutions for Project Euler

- Unify the header docstring, and add reference URLs to wikipedia
  or similar
- Fix docstrings to be properly multilined
- Add newlines where appropriate
- Add doctests where they were missing
- Remove doctests that test for the correct solution
- fix obvious spelling or grammar mistakes in comments and
  exception messages
- Fix line endings to be UNIX. This makes two of the files seem
  to have changed completely
- no functional changes in any of the solutions were done
  (except for the spelling fixes mentioned above)

* Fix docstrings and main function as per Style Guide

project_euler/problem_004/sol1.py

@@ -1,15 +1,21 @@
 """
-Problem:
-A palindromic number reads the same both ways. The largest palindrome made from
-the product of two 2-digit numbers is 9009 = 91 x 99.
+Project Euler Problem 4: https://projecteuler.net/problem=4
 
-Find the largest palindrome made from the product of two 3-digit numbers which
-is less than N.
+Largest palindrome product
+
+A palindromic number reads the same both ways. The largest palindrome made
+from the product of two 2-digit numbers is 9009 = 91 × 99.
+
+Find the largest palindrome made from the product of two 3-digit numbers.
+
+References:
+    - https://en.wikipedia.org/wiki/Palindromic_number
 """
 
 
 def solution(n: int = 998001) -> int:
-    """Returns the largest palindrome made from the product of two 3-digit
+    """
+    Returns the largest palindrome made from the product of two 3-digit
     numbers which is less than n.
 
     >>> solution(20000)
@@ -23,10 +29,10 @@ def solution(n: int = 998001) -> int:
     ...
     ValueError: That number is larger than our acceptable range.
     """
+
     # fetches the next number
     for number in range(n - 1, 9999, -1):
 
-        # converts number into string.
         str_number = str(number)
 
         # checks whether 'str_number' is a palindrome.
@@ -44,8 +50,4 @@ def solution(n: int = 998001) -> int:
 
 
 if __name__ == "__main__":
-    import doctest
-
-    doctest.testmod()
-
-    print(solution(int(input().strip())))
+    print(f"{solution() = }")

project_euler/problem_004/sol2.py

@@ -1,15 +1,21 @@
 """
-Problem:
-A palindromic number reads the same both ways. The largest palindrome made from
-the product of two 2-digit numbers is 9009 = 91 x 99.
+Project Euler Problem 4: https://projecteuler.net/problem=4
 
-Find the largest palindrome made from the product of two 3-digit numbers which
-is less than N.
+Largest palindrome product
+
+A palindromic number reads the same both ways. The largest palindrome made
+from the product of two 2-digit numbers is 9009 = 91 × 99.
+
+Find the largest palindrome made from the product of two 3-digit numbers.
+
+References:
+    - https://en.wikipedia.org/wiki/Palindromic_number
 """
 
 
 def solution(n: int = 998001) -> int:
-    """Returns the largest palindrome made from the product of two 3-digit
+    """
+    Returns the largest palindrome made from the product of two 3-digit
     numbers which is less than n.
 
     >>> solution(20000)
@@ -19,6 +25,7 @@ def solution(n: int = 998001) -> int:
     >>> solution(40000)
     39893
     """
+
     answer = 0
     for i in range(999, 99, -1):  # 3 digit numbers range from 999 down to 100
         for j in range(999, 99, -1):
@@ -29,4 +36,4 @@ def solution(n: int = 998001) -> int:
 
 
 if __name__ == "__main__":
-    print(solution(int(input().strip())))
+    print(f"{solution() = }")