# The Geppy String: Regex vs Iteration

We'll say that a lowercase 'g' in a string is "happy" if there is another 'g' immediately to its left or right. Return true if all the g's in the given string are happy.

gHappy("xxggxx") → true
gHappy("xxgxx") → false
gHappy("xxggyygxx") → false


I have written two functions to solve this problem, but I have some concerns:

• Of the one with Regex, I don't like all the special cases.
• Of the one with iteration, I don't like the weird helper method.

Both pass a fair number of tests and work correctly. Which one is better?

regex_geppy.rb

def geppy(string)
return true if ! string.include?('g')
return false if [0, 1].include?(string.length)
return false if string.length == 2 && string != 'gg'
return (not string.match("[^g]g[^g]"))
end


array_geppy.rb

def non_wrap_get(array, index)
index < 0 ? nil : array[index]
end

def geppy(string)
string
.chars
.each_with_index
.all? { |curr, i|
curr == 'g' ?
non_wrap_get(string, i - 1) == 'g'  || non_wrap_get(string, i + 1) == 'g'
: true
}
end


geppy_tests

geppy("xxggxx") #=> true
geppy("xxgxx") #=> false
geppy("xxggyygxx") #=> false
geppy("g") #=> false
geppy("ag") #=> false
geppy("gg") #=> true
geppy("") #=> true
geppy("ab") #=> true
geppy("aaaa") #=> true
geppy('g'*1000) #=> true


@200_success already showed a compact solution using regular expressions. As for the "array-solution", I think you missed the abstraction Enumerable#chunk:

def g_happy(s)
s.chars.chunk { |c| c }.all? { |c, cs| c == "g" ? cs.size > 1 : true }
end


Or .all? { |c, cs| cs != ["g"] }, whatever feels more declarative to you.

• Error: undefined method "itself" for string which version are you using? – Caridorc Jul 11 '15 at 9:07
• >= 2.2.0. Changed to a more portable block. – tokland Jul 11 '15 at 11:37

Regular expressions are the right tool to use for this kind of test. However, if you are going to use a regular expression to find lonely g characters, then you should use negative lookbehind and lookahead assertions instead of the negated character class [^g].

def geppy(str)
!/(?<!g)g(?!g)/.match(str)
end