Ruby Program to Check Palindrome String

You can check a palindrome in Ruby by comparing a string with its reverse using str == str.reverse. For example: puts 'madam' == 'madam'.reverse prints true.

Examples

Inputmadam

Outputtrue

Inputhello

Outputfalse

InputA man a plan a canal Panama

Outputfalse

How to Think About It

To check if a string is a palindrome, think about reading it forwards and backwards. If both are the same, the string is a palindrome. We can reverse the string and compare it to the original to decide.

Algorithm

1

Get the input string.

2

Reverse the string.

3

Compare the original string with the reversed string.

4

If both are equal, return true; otherwise, return false.

Code

ruby

puts 'Enter a string:'
str = gets.chomp
if str == str.reverse
  puts 'true'
else
  puts 'false'
end

Output

Enter a string:
madam
true

Dry Run

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

1

Input string

str = 'madam'

2

Reverse string

str.reverse = 'madam'

3

Compare original and reversed

'madam' == 'madam' is true

4

Print result

Output: true

Original String	Reversed String	Comparison Result
madam	madam	true

Why This Works

Step 1: Reverse the string

Using str.reverse creates a new string with characters in reverse order.

Step 2: Compare strings

The original string and reversed string are compared with == to check equality.

Step 3: Return result

If both strings match, the string is a palindrome, so we print true; otherwise, false.

Alternative Approaches

Using a loop to compare characters

ruby

puts 'Enter a string:'
str = gets.chomp
is_palindrome = true
(0...str.length / 2).each do |i|
  if str[i] != str[-i - 1]
    is_palindrome = false
    break
  end
end
puts is_palindrome

This method checks characters one by one without creating a reversed string, saving memory for very long strings.

Ignoring case and spaces

ruby

puts 'Enter a string:'
str = gets.chomp.downcase.gsub(/\s+/, '')
puts str == str.reverse

This approach ignores case and spaces, useful for phrases like 'A man a plan a canal Panama'.

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

Time Complexity

Reversing the string takes O(n) time where n is the string length, and comparing takes O(n) as well, so overall O(n).

Space Complexity

Reversing creates a new string of length n, so space complexity is O(n). The loop method uses O(1) extra space.

Which Approach is Fastest?

The direct reverse and compare method is simple and fast for most cases. The loop method saves space but is more complex.

Approach	Time	Space	Best For
Reverse and compare	O(n)	O(n)	Simple and readable code
Loop character comparison	O(n)	O(1)	Memory efficient for large strings
Ignoring case and spaces	O(n)	O(n)	Checking phrases ignoring formatting