=begin
two pointer:
* left
* right

left moves ->
right moves <-

* they move towards each other until they meet.
* if all characters are the same while they move towards each
other, then we have a palindrome.

     l     r
|b|a|n|a|n|a|


|b|a|
|b|a|n|
|b|a|n|a|
|b|a|n|a|n|
|b|a|n|a|n|a|

|a|n|
|a|n|a|
|a|n|a|n|
|a|n|a|n|a|

|n|a|
|n|a|n|
|n|a|n|a|

|a|n|a|

recursive solution
base case:

* s is empty

if s[0] == s[-1]
  run(s[1..-2])
end
=end

def assert_equal(x, y)
  return puts "PASS" if x == y
  puts "FAIL: expected #{x}, got #{y}"
end

class Solution
  def self.palindrome?(string)
    return false if string.nil? || string.empty?

    string == string.reverse
  end

  def self.run(string)
    max = ""
    for l in (0..string.size)
      for r in (l+1..string.size)
        candidate = string[l..r]
        if palindrome?(candidate) && candidate.size > max.size
          max = candidate
        end
      end
    end
    max
  end
end

assert_equal 'anana', Solution.run('banana')
assert_equal 'illi', Solution.run('million')
assert_equal 'racecar', Solution.run('tracecars')
assert_equal 'tacocat', Solution.run('loltacocatmom')