Unify O(sqrt(N)) is_prime functions under project_euler (#6258)

* fixes #5434

* fixes broken solution

* removes assert

* removes assert

* Apply suggestions from code review

Co-authored-by: John Law <johnlaw.po@gmail.com>

* Update project_euler/problem_003/sol1.py

Co-authored-by: John Law <johnlaw.po@gmail.com>

project_euler/problem_058/sol1.py

@@ -33,29 +33,46 @@ So we check individually each one of these before incrementing our
 count of current primes.
 
 """
-from math import isqrt
+import math
 
 
-def is_prime(number: int) -> int:
-    """
-    Returns whether the given number is prime or not
+def is_prime(number: int) -> bool:
+    """Checks to see if a number is a prime in O(sqrt(n)).
+
+    A number is prime if it has exactly two factors: 1 and itself.
+
+    >>> is_prime(0)
+    False
     >>> is_prime(1)
-    0
-    >>> is_prime(17)
-    1
-    >>> is_prime(10000)
-    0
+    False
+    >>> is_prime(2)
+    True
+    >>> is_prime(3)
+    True
+    >>> is_prime(27)
+    False
+    >>> is_prime(87)
+    False
+    >>> is_prime(563)
+    True
+    >>> is_prime(2999)
+    True
+    >>> is_prime(67483)
+    False
     """
-    if number == 1:
-        return 0
 
-    if number % 2 == 0 and number > 2:
-        return 0
+    if 1 < number < 4:
+        # 2 and 3 are primes
+        return True
+    elif number < 2 or number % 2 == 0 or number % 3 == 0:
+        # Negatives, 0, 1, all even numbers, all multiples of 3 are not primes
+        return False
 
-    for i in range(3, isqrt(number) + 1, 2):
-        if number % i == 0:
-            return 0
-    return 1
+    # All primes number are in format of 6k +/- 1
+    for i in range(5, int(math.sqrt(number) + 1), 6):
+        if number % i == 0 or number % (i + 2) == 0:
+            return False
+    return True
 
 
 def solution(ratio: float = 0.1) -> int: