laboratory/experiments/go/shuffle-elements/shuffle.go

package main

type shuffleDirection int

const (
	left shuffleDirection = iota
	right
)

// shuffleFuncOne creates a new list where an element in one position is repositioned
// to the index of another element. All affected elements then shuffleFuncOne one place to the left
// or right depending on the direction of the move.
func shuffleFuncOne(list []any, oldPos, newPos int) []any {
	var direction shuffleDirection

	if newPos < oldPos {
		direction = right
	} else {
		direction = left
	}

	newList := make([]any, len(list))

	for i := range list {
		switch {
		case (direction == right) && (i < newPos || i > oldPos):
			newList[i] = list[i]
		case (direction == right) && (i == oldPos):
			newList[newPos] = list[i]
		case (direction == right):
			newList[i+1] = list[i]
		case (direction == left) && (i < oldPos || i > newPos):
			newList[i] = list[i]
		case (direction == left) && (i == oldPos):
			newList[newPos] = list[i]
		case (direction == left):
			newList[i-1] = list[i]
		}
	}

	return newList
}

// shuffleFuncTwo produces the same output as shuffleFuncOne using a slightly different method.
// The original slice is copied into a new slice and the element is immediately placed in the new
// position. The for loop then only focuses on the elements in range between the two positions and
// are shuffled left or right as required.
func shuffleFuncTwo(list []any, oldPos, newPos int) []any {
	newList := make([]any, len(list))

	copy(newList, list)

	newList[newPos] = list[oldPos]

	if newPos < oldPos {
		for i := newPos; i <= oldPos; i++ {
			if i != oldPos {
				newList[i+1] = list[i]
			}
		}

		return newList
	}

	for i := oldPos; i <= newPos; i++ {
		if i != oldPos {
			newList[i-1] = list[i]
		}
	}

	return newList
}