feat(day 147): add leap year calculator using standard divisibility rules

Author: JohnSunny21

FreeCodeCamp/CodingQ/LeapYearCalculator.py

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+"""  
+Leap Year Calculator
+Given an integer year, determine whether it is a leap year.
+
+A year is a leap year if it satisfies the following rules:
+
+The year is evenly divisible by 4, and
+The year is not evenly divisible by 100, unless
+The year is evenly divisible by 400.
+"""
+
+import unittest
+
+class LeapYearCalculatorTest(unittest.TestCase):
+
+    def test1(self):
+        self.assertEqual(is_leap_year(2024), True)
+
+    def test2(self):
+        self.assertEqual(is_leap_year(2023), False)
+
+    def test3(self):
+        self.assertEqual(is_leap_year(2100), False)
+
+    def test4(self):
+        self.assertEqual(is_leap_year(2000), True)
+
+    def test5(self):
+        self.assertEqual(is_leap_year(1999), False)
+
+    def test6(self):
+        self.assertEqual(is_leap_year(2040), True)
+
+    def test7(self):
+        self.assertEqual(is_leap_year(2026), False)
+
+
+
+def is_leap_year(year):
+
+    return (year % 4 == 0 and (year % 100 != 0 or year % 400 == 0))
+
+"""
+1. Divisible by 4 -> candidate for leap year.
+2. Divisible by 100 -> normally not a leap year (exception case).
+3. Divisible by 400 -> is a leap year (special override).
+
+So: 
+-> 2000 -> leap year (divisible by 400).
+-> 1900 -> not a leap year (divisible by 100 but not 400).
+-> 2024 -> leap year (divisble by 4, not by 100).
+-> 2023 -> not a leap year (not divisible by 4).
+
+==> Year = 2024
+ -> 2024 % 4 == 0 -> True
+ -> 2024 % 100 != 0 -> True
+ -> Whole condition -> True -> Leap Year.
+
+==> Year - 1900
+ -> 1900 % 4 == 0 -> True
+ -> 1900 % 100 != 0 -> False
+ -> 1900 % 400 == 0 -> False
+ -> Inner condition -> False -> Not leap year.
+
+==> Year = 2000 
+ -> 2000 % 4 == 0 -> True
+ -> 2000 % 100 != 0 -> False
+ -> 2000 % 400 == 0 -> True
+ -> Inner condition -> True -> Leap Year.
+
+
+-> Divisible by 4 -> candidate
+-> Centuries (divisible by 100) are excluded.
+-> Exceptioon: centuries divisible by 400 are included.
+"""
+
+if __name__ == "__main__":
+    print(is_leap_year(2026))
+    unittest.main()