Ruby Program to Reverse a String with Examples and Explanation

You can reverse a string in Ruby using the reverse method like this: reversed = original_string.reverse.

Examples

Inputhello

Outputolleh

InputRuby

OutputybuR

Input

Output

How to Think About It

To reverse a string, think of reading the characters from the end to the start. You take the last character first, then the second last, and so on until you reach the first character. This creates a new string with characters in reverse order.

Algorithm

1

Get the input string.

2

Start from the last character of the string.

3

Collect characters moving backward to the first character.

4

Form a new string from these collected characters.

5

Return or print the new reversed string.

Code

ruby

puts "Enter a string:"
input = gets.chomp
reversed = input.reverse
puts "Reversed string: #{reversed}"

Output

Enter a string:
hello
Reversed string: olleh

Dry Run

Let's trace the input 'hello' through the code

1

Input received

input = 'hello'

2

Reverse method called

reversed = 'hello'.reverse

3

Reverse method result

reversed = 'olleh'

4

Output printed

Print 'Reversed string: olleh'

Step	Input	Output
1	hello	hello
2	hello	olleh
3	olleh	olleh

Why This Works

Step 1: Using the reverse method

The reverse method in Ruby returns a new string with characters in the opposite order.

Step 2: No manual looping needed

Ruby handles the character order internally, so you don't need to write loops to reverse the string.

Step 3: Output the reversed string

We print the reversed string using puts to show the result to the user.

Alternative Approaches

Manual loop with each_char

ruby

puts "Enter a string:"
input = gets.chomp
reversed = ""
input.each_char { |char| reversed = char + reversed }
puts "Reversed string: #{reversed}"

This method builds the reversed string by adding each character to the front, which is more manual but shows the process clearly.

Using array reverse

ruby

puts "Enter a string:"
input = gets.chomp
reversed = input.chars.reverse.join
puts "Reversed string: #{reversed}"

This converts the string to an array of characters, reverses the array, then joins it back to a string. Slightly longer but useful to understand arrays.

Complexity: O(n) time, O(n) space

Time Complexity

The reverse method processes each character once, so it takes time proportional to the string length, O(n).

Space Complexity

It creates a new string to hold the reversed characters, so space used is also O(n).

Which Approach is Fastest?

Using the built-in reverse method is fastest and most readable compared to manual loops or array conversions.

Approach	Time	Space	Best For
Built-in reverse method	O(n)	O(n)	Simple and fast string reversal
Manual loop with each_char	O(n)	O(n)	Learning how reversal works step-by-step
Array reverse and join	O(n)	O(n)	When working with arrays and strings together