Longest Palindromic Substring in Ruby

Longest Palindromic

Substring in Ruby

Welcome to the Longest Palindromic Substring in Ruby page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

def expand(s, l, r)
  while l >= 0 && r < s.length && s[l] == s[r]
    l -= 1
    r += 1
  end

  [l + 1, r - l - 1] # start, length
end

def longest_palindromic_substring(s)
  return if s.to_s.empty?

  best_start = 0
  best_len = 1

  s.length.times do |i|
    start1, len1 = expand(s, i, i)
    start2, len2 = expand(s, i, i + 1)

    start, len = (len1 > len2) ? [start1, len1] : [start2, len2]

    if len > best_len
      best_start, best_len = start, len
    end
  end

  s.slice(best_start, best_len)
end

input = ARGV.first
result = longest_palindromic_substring(input)

abort("Usage: please provide a string that contains at least one palindrome") if result.nil? || result.length <= 1

puts result

Longest Palindromic Substring in Ruby was written by:

• Ștefan-Iulian Alecu

If you see anything you'd like to change or update, please consider contributing.

How to Implement the Solution

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How to Run the Solution

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