Ruby Program to Check Palindrome Number

You can check a palindrome number in Ruby by converting the number to a string and comparing it with its reverse using num.to_s == num.to_s.reverse.

Examples

Input121

Output121 is a palindrome number.

Input123

Output123 is not a palindrome number.

Input0

Output0 is a palindrome number.

How to Think About It

To check if a number is a palindrome, think of it like reading a word forwards and backwards. Convert the number to a string, then compare the string with its reverse. If both are the same, the number is a palindrome.

Algorithm

1

Get the input number.

2

Convert the number to a string.

3

Reverse the string.

4

Compare the original string with the reversed string.

5

If they are equal, the number is a palindrome; otherwise, it is not.

6

Print the result.

Code

ruby

puts "Enter a number:"
num = gets.chomp
if num == num.reverse
  puts "#{num} is a palindrome number."
else
  puts "#{num} is not a palindrome number."
end

Output

Enter a number:
121
121 is a palindrome number.

Dry Run

Let's trace the input 121 through the code

1

Input number

num = "121"

2

Reverse string

num.reverse = "121"

3

Compare strings

"121" == "121" is true

4

Print result

Output: "121 is a palindrome number."

num	num.reverse	Comparison Result
121	121	true

Why This Works

Step 1: Convert number to string

We use gets.chomp to read input as a string so we can easily reverse it.

Step 2: Reverse the string

Using num.reverse creates a reversed copy of the input string.

Step 3: Compare original and reversed

If the original string equals the reversed string, the number reads the same forwards and backwards, so it is a palindrome.

Alternative Approaches

Using integer reversal

ruby

puts "Enter a number:"
num = gets.to_i
original = num
reversed = 0
while num > 0
  reversed = reversed * 10 + num % 10
  num /= 10
end
if original == reversed
  puts "#{original} is a palindrome number."
else
  puts "#{original} is not a palindrome number."
end

This method works with integers directly without converting to string but is more complex.

Using recursion to check palindrome

ruby

def palindrome?(str)
  return true if str.length <= 1
  return false if str[0] != str[-1]
  palindrome?(str[1..-2])
end
puts "Enter a number:"
num = gets.chomp
if palindrome?(num)
  puts "#{num} is a palindrome number."
else
  puts "#{num} is not a palindrome number."
end

This recursive method checks characters from outside in but is less efficient for large inputs.

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

Time Complexity

Reversing the string takes O(n) time where n is the number of digits, and comparison also takes O(n).

Space Complexity

The reversed string requires O(n) extra space to store the reversed copy.

Which Approach is Fastest?

The string reversal method is simple and fast for typical inputs, while integer reversal avoids extra string space but uses more steps.

Approach	Time	Space	Best For
String reversal	O(n)	O(n)	Simplicity and readability
Integer reversal	O(n)	O(1)	Memory efficiency with numeric operations
Recursive check	O(n)	O(n)	Learning recursion, less practical