The trend kata is an exercise in determining the 'trend' of a series of numbers. The algorithm is weighted towards non-zero values and numbers in the series that are changing. A value of zero and numbers in sequence that are the same value, are given less weight in the calculation. The algorithm will be a summing of results, for each pair within the list, shifted by one (1).
This algorithm, will expect a list of numbers... whole numbers and/or decimals.
- if the supplied list is empty or does not exist (null), then the trend calculator should return null.
- if the list contains only a single value, then the trend calculator should return a value of zero (0).
- the resulting trend will always start with a value of zero (0).
- the first pair will contain the first two numbers in the list
- the second pair will contain the second and third number in the list (and so on, until the list is completely processed).
- the final pair, will be the last two numbers in the list.
- the order of the list will be determined by the original order passed to the calculator. No additional sorting will be required.
The following calculation will be applied to each pair. Pairs will be denoted as [p1, p2]
- if p1 equals zero and p2 > 0, the value for the pair will be 1.0
- if p1 equals p2, the value for the pair will be 0.0
- otherwise, the value for the pair will be (p2-p1)/p1.
- The result of each pair calculation will be summed, returning the trend value.