Add style improvements to solutions for Project Euler Problem 04 (TheAlgorithms#2945)

* Fix typehints in project_euler/problem01

Squashed commit of the following:

commit 6801d07
Author: Archaengel <[email protected]>
Date:   Mon Oct 5 16:40:10 2020 -0700

    Fix typehints in project_euler/problem01

commit 29afc3a
Author: Archaengel <[email protected]>
Date:   Mon Oct 5 15:06:34 2020 -0700

    Add typehints and default argument for project_euler/problem_01

* Add default args, typehints, and expand variable names for PE prob 02

* Add style improvements for first solution of PE Problem 02

* Add default arg and typehints for second solution of PE Problem 02

* Add default arg for third solution of PE Problem 02

* Add style improvements for 1st soln of PE problem 03

* Add default arg and typehints for 2nd soln of PE problem 03

* Add default arg for 3rd soln of PE problem 03

* Remove unnecessary newlines

* Remove unnecessary newlines

* Fix end of file for 2nd soln in PE problem 03

* Add style improvements to solutions for PE problem 04

* Restore original newlines in soln for PE problem 04

* Fix punctuation in docstring for PE problem 04

* Restore solution bodies for PE problem 04

* Expand variable names for 2nd soln of PE problem 04

Author: archaengel

Diff for: project_euler/problem_04/sol1.py

@@ -8,7 +8,7 @@
 """
 
 
-def solution(n):
+def solution(n: int = 998001) -> int:
     """Returns the largest palindrome made from the product of two 3-digit
     numbers which is less than n.
 

Diff for: project_euler/problem_04/sol2.py

@@ -8,7 +8,7 @@
 """
 
 
-def solution(n):
+def solution(n: int = 998001) -> int:
     """Returns the largest palindrome made from the product of two 3-digit
     numbers which is less than n.
 
@@ -22,8 +22,8 @@ def solution(n):
     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):
-            t = str(i * j)
-            if t == t[::-1] and i * j < n:
+            product_string = str(i * j)
+            if product_string == product_string[::-1] and i * j < n:
                 answer = max(answer, i * j)
     return answer