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module TreeSpell
# Changes a word with one of four actions:
# insertion, substitution, deletion and transposition.
class ChangeWord
# initialize with input string
def initialize(input)
@input = input
@len = input.length
end
# insert char after index of i_place
def insertion(i_place, char)
@word = input.dup
return char + word if i_place == 0
return word + char if i_place == len - 1
word.insert(i_place + 1, char)
end
# substitute char at index of i_place
def substitution(i_place, char)
@word = input.dup
word[i_place] = char
word
end
# delete character at index of i_place
def deletion(i_place)
@word = input.dup
word.slice!(i_place)
word
end
# transpose char at i_place with char at i_place + direction
# if i_place + direction is out of bounds just swap in other direction
def transposition(i_place, direction)
@word = input.dup
w = word.dup
return swap_first_two(w) if i_place + direction < 0
return swap_last_two(w) if i_place + direction >= len
swap_two(w, i_place, direction)
w
end
private
attr_accessor :word, :input, :len
def swap_first_two(w)
w[1] + w[0] + word[2..-1]
end
def swap_last_two(w)
w[0...(len - 2)] + word[len - 1] + word[len - 2]
end
def swap_two(w, i_place, direction)
w[i_place] = word[i_place + direction]
w[i_place + direction] = word[i_place]
end
end
end
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