A string is called lucky if no two consecutive characters are equal. How many lucky strings can you get by reordering letters in a given string *s*? *s* itself counts, too, if it is lucky. 1 <= length(*s*) <= 10 *s[i]* is in 'a'..'z' Example 1 input: "ab" output: 2 Two lucky strings - "ab" and "ba". Example 2 input: "aaab" output: 0 It's impossi…

lucky_strings.rb

def permutations(string)
  permutations = string.split('').permutation.map(&:join).uniq
end

def lucky_strings(string)
  permutations(string).select{|s| s.squeeze == s}.count
end

lucky_strings('ab') #=> 2
lucky_strings('aaab') #=> 0
lucky_strings('aabbbaa') #=> 1
lucky_strings('abcdefghij') #=> 3628800