In how many ways can the letters A, B, C and D be arranged so that no letter is adjacent to any letter that comes immediately before it or immediately after it alphabetically?
I understand there are 4! ways to arrange the letters A, B, C, D without any constraints.
What method should I use here? Complementary or constructive?
I will start with complementary.
There are 4! ways w/out constraints.
Let's see how many ways there are to arrange the letters so that every letter IS adjacent to the letter that comes immediately before or immediately after it.
o _ O How will I find this? Help is appreciated! :D
I might not be correct, but I think it's 2. I don't have time to show a solution, but I will about 30 min. later.