exercism - Flatten Array

flatten1.go

package flatten

// BenchmarkFlatten-8        244364              4568 ns/op            3232 B/op         80 allocs/op
func Flatten(nested interface{}) []interface{} {
	flattened := []interface{}{}

	switch x := nested.(type) {
	case []interface{}:
		for _, v := range x {
			flattened = append(flattened, Flatten(v)...)
		}
	default:
		if x != nil {
			flattened = append(flattened, x)
		}
	}

	return flattened
}

flatten2.go

package flatten

// BenchmarkFlatten-8        340998              3304 ns/op            3248 B/op         43 allocs/op
func Flatten(nested interface{}) []interface{} {
	flattened := []interface{}{}

	var v interface{}
	array := nested.([]interface{})
	for 0 < len(array) {
		v, array = array[0], array[1:]
		switch x := v.(type) {
		case []interface{}:
			array = append(x, array...)
			continue
		case interface{}:
			flattened = append(flattened, v)
		}
	}

	return flattened
}

flatten3.go

package flatten

type arrayStackItem struct {
	index int
	array []interface{}
}

// BenchmarkFlatten-8        486426              2328 ns/op            2256 B/op         33 allocs/op
func Flatten(nested interface{}) []interface{} {
	stack := []arrayStackItem{}

	flattened := []interface{}{}

	i, array := 0, nested.([]interface{})
	for {
		if i >= len(array) {
			if len(stack) > 0 {
				var item arrayStackItem
				item, stack = stack[len(stack)-1], stack[:len(stack)-1]
				i, array = item.index, item.array
				continue
			}
			if i >= len(array) {
				break
			}
		}

		v := array[i]
		i++
		switch x := v.(type) {
		case []interface{}:
			stack = append(stack, arrayStackItem{i, array})
			i, array = 0, x
			continue
		case interface{}:
			flattened = append(flattened, x)
		}
	}

	return flattened
}