Fix code style for Project Euler problems:

- 13, 17, 21
- Default args
- Type hints
- File path

Author: dhruvmanila

project_euler/problem_13/sol1.py

@@ -1,30 +1,30 @@
 """
+Problem 13: https://projecteuler.net/problem=13
+
 Problem Statement:
 Work out the first ten digits of the sum of the following one-hundred 50-digit
 numbers.
 """
+import os
 
 
-def solution(array):
-    """Returns the first ten digits of the sum of the array elements.
+def solution():
+    """
+    Returns the first ten digits of the sum of the array elements
+    from the file num.txt
 
-    >>> import os
-    >>> sum = 0
-    >>> array = []
-    >>> with open(os.path.dirname(__file__) + "/num.txt","r") as f:
-    ...     for line in f:
-    ...         array.append(int(line))
-    ...
-    >>> solution(array)
+    >>> solution()
     '5537376230'
     """
+    array = []
+
+    file_path = os.path.join(os.path.dirname(__file__), "num.txt")
+    with open(file_path, "r") as file_hand:
+        for line in file_hand:
+            array.append(int(line))
+
     return str(sum(array))[:10]
 
 
 if __name__ == "__main__":
-    n = int(input().strip())
-
-    array = []
-    for i in range(n):
-        array.append(int(input().strip()))
-    print(solution(array))
+    print(solution())

project_euler/problem_17/sol1.py

@@ -1,6 +1,6 @@
 """
 Number letter counts
-Problem 17
+Problem 17: https://projecteuler.net/problem=17
 
 If the numbers 1 to 5 are written out in words: one, two, three, four, five,
 then there are 3 + 3 + 5 + 4 + 4 = 19 letters used in total.
@@ -16,7 +16,7 @@
 """
 
 
-def solution(n):
+def solution(n: int = 1000) -> int:
     """Returns the number of letters used to write all numbers from 1 to n.
     where n is lower or equals to 1000.
     >>> solution(1000)

project_euler/problem_21/sol1.py

@@ -1,5 +1,3 @@
-from math import sqrt
-
 """
 Amicable Numbers
 Problem 21
@@ -15,9 +13,10 @@
 
 Evaluate the sum of all the amicable numbers under 10000.
 """
+from math import sqrt
 
 
-def sum_of_divisors(n):
+def sum_of_divisors(n: int) -> int:
     total = 0
     for i in range(1, int(sqrt(n) + 1)):
         if n % i == 0 and i != sqrt(n):
@@ -27,7 +26,7 @@ def sum_of_divisors(n):
     return total - n
 
 
-def solution(n):
+def solution(n: int = 10000) -> int:
     """Returns the sum of all the amicable numbers under n.
 
     >>> solution(10000)