In this challenge, you will be given a string. You must remove characters until the string is made up of any two alternating characters. When you choose a character to remove, all instances of that character must be removed. Your goal is to create the longest string possible that contains just two alternating letters.
As an example, consider the string abaacdabd. If you delete the character a, you will be left with the string bcdbd. Now, removing the character c leaves you with a valid string bdbd having a length of 4. Removing either b or d at any point would not result in a valid string.
Given a string , convert it to the longest possible string made up only of alternating characters. Print the length of string on a new line. If no string can be formed, print instead.
The first line contains a single integer denoting the length of .
The second line contains string .
Print a single integer denoting the maximum length of for the given ; if it is not possible to form string , print instead.
The characters present in are a, b, e, and f. This means that must consist of two of those characters and we must delete two others. Our choices for characters to leave are [a,b], [a,e], [a, f], [b, e], [b, f] and [e, f].
If we delete e and f, the resulting string is babab. This is a valid as there are only two distinct characters (a and b), and they are alternating within the string.
If we delete a and f, the resulting string is bebeeeb. This is not a valid string because there are consecutive e's present. Removing them would leave consecutive b's, so this fails to produce a valid string .