Class: TTY2::Prompt::Distance

Inherits:
Object
  • Object
show all
Defined in:
lib/tty2/prompt/distance.rb

Overview

A class responsible for string comparison

Instance Method Summary collapse

Instance Method Details

#distance(first, second) ⇒ Object

Calculate the optimal string alignment distance



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# File 'lib/tty2/prompt/distance.rb', line 10

def distance(first, second)
  distances = []
  rows      = first.to_s.length
  cols      = second.to_s.length

  0.upto(rows) do |index|
    distances << [index] + [0] * cols
  end
  distances[0] = 0.upto(cols).to_a

  1.upto(rows) do |first_index|
    1.upto(cols) do |second_index|
      first_char  = first[first_index - 1]
      second_char = second[second_index - 1]
      cost        = first_char == second_char ? 0 : 1

      distances[first_index][second_index] = [
        distances[first_index - 1][second_index], # deletion
        distances[first_index][second_index - 1],     # insertion
        distances[first_index - 1][second_index - 1]  # substitution
      ].min + cost

      if first_index > 1 && second_index > 1
        first_previous_char = first[first_index - 2]
        second_previous_char = second[second_index - 2]
        if first_char == second_previous_char && second_char == first_previous_char
          distances[first_index][second_index] = [
            distances[first_index][second_index],
            distances[first_index - 2][second_index - 2] + 1 # transposition
          ].min
        end
      end

    end
  end
  distances[rows][cols]
end