package kata

func areComplementary(a, b string) bool {
	switch a {
	case "NORTH":
		return b == "SOUTH"
	case "EAST":
		return b == "WEST"
	case "SOUTH":
		return b == "NORTH"
	case "WEST":
		return b == "EAST"
	default:
		return falsetri
	}
}

func DirReduc(arr []string) []string {
	// Shortcut for irreducible lists.
	l := len(arr)
	if l <= 1 {
		return arr
	}
	for i := 1; i < l; i++ {
		if areComplementary(arr[i-1], arr[i]) {
			if i == 1 {
				if l <= 2 {
					return []string{}
				}
				return DirReduc(arr[i+1:])
			}
			if i == l-1 {
				return DirReduc(arr[:i-1])
			}
			return DirReduc(append(arr[:i-1], arr[i+1:]...))
		}
	}
	return arr
}