func (s *service) PermuteBy(list spec.PermutationList, delta int) error {
if delta < 1 {
return nil
}
newIndizes, err := createIndizesWithDelta(list, delta)
if err != nil {
return maskAny(err)
}
list.SetIndizes(newIndizes)
return nil
}
func permuteValues(list spec.PermutationList) []interface{} {
permutedValues := make([]interface{}, len(list.GetIndizes()))
for i, index := range list.GetIndizes() {
permutedValues[i] = list.GetRawValues()[index]
}
return permutedValues
}
func createIndizesWithDelta(list spec.PermutationList, delta int) ([]int, error) {
// Initialize scope variables.
base := len(list.GetRawValues())
newIndizes := list.GetIndizes()
operation := 0
// Check for the initial situation. This is special and the only exception
// within the algorithm.
if len(newIndizes) == 0 {
newIndizes = append(newIndizes, 0)
operation++
}
for {
// Check amount of operations in the first place. That way the initial
// situation as well as all other operations are covered.
operation++
if operation > delta {
break
}
// Increment the least significant digit. That is, the right most index.
// This is the only incrementation being done on the index.
i := len(newIndizes) - 1
lsd := newIndizes[i]
lsd++
newIndizes[i] = lsd
// Cap the indizes and shift them if necessary. In case the least
// significant digit was incremented above the base capacity, indizes need
// to be shifted from right to left. This is like counting a number.
var msdShifted bool
newIndizes, msdShifted = shiftIndizes(newIndizes, base)
if msdShifted {
// Make sure the permutation does not growth more than allowed.
if len(newIndizes)+1 > list.GetMaxGrowth() {
return nil, maskAny(maxGrowthReachedError)
}
// In case all the indizes where shifted, we zeroed out all indizes. Then
// we need to prepend another zero as new most significant digit of the
// index.
newIndizes = prepend(newIndizes, 0, 0)
}
}
return newIndizes, nil
}
