Calculates the sum of elements in a list between two indices using recursion.

CalculateSumBetweenIndices.cs

/// <summary>
/// Calculates the sum of elements in a list between two indices using recursion.
/// </summary>
/// <param name="numbers">The list of numbers.</param>
/// <param name="startIndex">The starting index for the sum.</param>
/// <param name="endIndex">The ending index for the sum.</param>
/// <param name="accumulatedSum">The current accumulated sum (used for recursion).</param>
/// <returns>The sum of elements between the specified indices.</returns>
public static int CalculateSumBetweenIndices(List<int> numbers, int startIndex, int endIndex, int accumulatedSum = 0)
{
    if (startIndex > endIndex) return accumulatedSum;
    
    if (startIndex < 0 || startIndex >= numbers.Count || endIndex < 0 || endIndex >= numbers.Count)
    {
        throw new ArgumentOutOfRangeException("Indices are out of the range of the list.");
    }
    
    accumulatedSum += numbers[startIndex];
    
    return CalculateSumBetweenIndices(numbers, startIndex + 1, endIndex, accumulatedSum);
}