Prints all the permutation of the given string

permutation.rb

def permutation(prefix, str)
  n = str.length
  if n == 0
    p prefix
  else
    for i in 0..n-1 do
      if i == 0
        perm("#{prefix}#{str[i]}", str[i+1..n-1])
      else
        perm("#{prefix}#{str[i]}", "#{str[0..i-1]}#{str[i+1..n-1]}")
      end
    end
  end
end

permutation('', 'abc')