Longest Common Subsequence in Ruby

Longest Common

Subsequence in Ruby

Welcome to the Longest Common Subsequence 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

# frozen_string_literal: true

USAGE = 'Usage: please provide two lists in the format "1, 2, 3, 4, 5"'

def usage!
  warn USAGE
  exit 1
end

def parse_list(str)
  str.split(",").map { Integer(it.strip) }
rescue ArgumentError, NoMethodError
  usage!
end

def lcs(a, b)
  n = a.size
  m = b.size

  dp = Array.new(n + 1) { Array.new(m + 1, 0) }

  (1..n).each do |i|
    (1..m).each do |j|
      dp[i][j] = if a[i - 1] == b[j - 1]
        dp[i - 1][j - 1] + 1
      else
        [dp[i - 1][j], dp[i][j - 1]].max
      end
    end
  end

  i, j = n, m
  result = []

  while i > 0 && j > 0
    if a[i - 1] == b[j - 1]
      result << a[i - 1]
      i -= 1
      j -= 1
    elsif dp[i - 1][j] >= dp[i][j - 1]
      i -= 1
    else
      j -= 1
    end
  end

  result.reverse
end

a_str, b_str = ARGV
usage! if a_str.nil? || b_str.nil? || a_str.strip.empty? || b_str.strip.empty?

a = parse_list(a_str)
b = parse_list(b_str)

puts lcs(a, b).join(", ")

Longest Common Subsequence 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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