Reverse a string in Ruby

Question

How do you reverse a string in Ruby? I know about string#reverse. I\'m interested in understanding how to write it in pure Ruby, preferably an in-place solution.

Answer 1

Use

def reverse_string(string) # Method reverse_string with parameter 'string'.
  loop = string.length # int loop is equal to the string's length.
  word = '' # This is what we will use to output the reversed word.
  while loop > 0 # while loop is greater than 0, subtract loop by 1 and add the string's index of loop to 'word'.
    loop -= 1 # Subtract 1 from loop.
    word += string[loop] # Add the index with the int loop to word.
  end # End while loop.
  return word # Return the reversed word.
end # End the method.

Answer 2

string = "This is my string"
string_arr = string.split('')
n = string_arr.length
new_arr = Array.new

17.times do |i|
  new_arr << string_arr.values_at(n - i)
end

reversed_string = new_arr.flatten.join('')
=> "gnirts ym si sihT"

Answer 3

There's already an inplace reverse method, called "reverse!":

$ a = "abc"
$ a.reverse!
$ puts a
cba

If you want to do this manually try this (but it will probably not be multibyte-safe, eg UTF-8), and it will be slower:

class String
  def reverse_inplace!
    half_length = self.length / 2
    half_length.times {|i| self[i], self[-i-1] = self[-i-1], self[i] }
    self
  end
end

This swaps every byte from the beginning with every byte from the end until both indexes meet at the center:

$ a = "abcd"
$ a.reverse_inplace!
$ puts a
dcba

Answer 4

Consider looking at how Rubinius implements the method - they implement much of the core library in Ruby itself, and I wouldn't be surprised if String#reverse and String#reverse! is implemented in Ruby.

Answer 5

This is the solution that made the most sense to me as a ruby beginner

def reverse(string)
  reversed_string = ''

  i = 0
  while i < string.length
    reversed_string = string[i] + reversed_string
    i += 1
  end

  reversed_string
end

p reverse("helter skelter")

Answer 6

Hard to read one-liner,

def reverse(a)
    (0...(a.length/2)).each {|i| a[i], a[a.length-i-1]=a[a.length-i-1], a[i]}
    return a
end