using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        DateTime d1 = new DateTime(2019, 11, 21, 0, 0, 0);

        DateTime d2 = new DateTime(2020, 11, 21, 0, 0, 0);

        DateTime d3 = new DateTime(2021, 11, 21, 0, 0, 0);

        var firstRange = NumberOfLeapYears(d1, d2);

        var secondRange = NumberOfLeapYears(d2, d3);

        Console.WriteLine($"Expected 1: Actual: {firstRange.Count}, First Range should have 1 leap year");

        Console.WriteLine($"Expected 1: Actual: {secondRange.Count}, Second Range should have 1 leap year");

        var firstRangeRefactor = NumberOfLeapYearsRefactor(d1, d2);

        var secondRangeRefactor = NumberOfLeapYearsRefactor(d2, d3);

        Console.WriteLine($"Expected 1: Actual: {firstRangeRefactor.Count}, First Range Refactor should have 1 leap year");

        Console.WriteLine($"Expected 1: Actual: {secondRangeRefactor.Count}, Second Range Refactor should have 1 leap year");

        var d4 = new DateTime(2020, 12, 21, 0, 0, 0);

        var sameYearOriginal = NumberOfLeapYears(d1, d2);

        var sameYearRefactor = NumberOfLeapYearsRefactor(d2, d3);

        Console.WriteLine($"Expected 1: Actual: {sameYearOriginal.Count}, Same Year Range (Original Imp) should have 1 leap year");

        Console.WriteLine($"Expected 1: Actual: {sameYearRefactor.Count}, Same Year Range (Refactor Imp) should have 1 leap year");

    }

    public static List<int> NumberOfLeapYears(DateTime effectiveDate, DateTime expirationDate) 

    {

        List<int> numberOfLeapYears = new List<int>();

​

        for (var dt = effectiveDate.Year; dt <= expirationDate.Year; dt++)

        {

            if (DateTime.IsLeapYear(dt))

            {

                DateTime LeapMonth = new DateTime(dt, 2, 29, 0, 0, 0);

​

                if (LeapMonth > effectiveDate && LeapMonth <= expirationDate)

                {

                    numberOfLeapYears.Add(dt);

                }

            }

        }

        return numberOfLeapYears;

    }

    public static List<int> NumberOfLeapYearsRefactor(DateTime effectiveDate, DateTime expirationDate) 

    {

        List<int> numberOfLeapYears = new List<int>();

​

        for (var dt = effectiveDate.Year; dt <= expirationDate.Year; dt++)

        {

            if (DateTime.IsLeapYear(dt))

            {

                numberOfLeapYears.Add(dt);

            }

        }

        return numberOfLeapYears;

    }

}