How do I think about recursion in programming?

[shivajikobardan]

Homework Statement

thinking about recursion in programming for palindrome checker

Relevant Equations

none

I got the idea for problems like factorials or finding sum from 1 to n, where there's a pattern visible. Like this:

Source:https://99x.io/blog/recursion-is-not-hard-here-is-the-right-way-to-think

I got it for things like addition, subtraction, division, multiplication of two numbers as well.

eg: a+b

=a+b-1+1

=SUM(a+1,b-1)

Now, I am wondering how it'll be for finding a palindrome of a number? I've a solution but I'm not understanding how we came towards it. I'm looking for how to come towards a solution than a solution itself.

A number is palindrome if it's same as it's reversed. eg: REFER, RADAR, NOON etc are palindrome strings.

I'm unable to grasp a pattern here. Also, please share some books based on mathematics(Not full books but part of book on recursion) that have exercises of recursive functions. I think that'd help greatly with recursion.

 

[FactChecker]

If the two ends are equal then remove them and call the function with the smaller string.

 

[FactChecker]

You don't necessarily have to see a pattern to use recursion. As long as the recursive call is applied to a smaller problem of the same nature, you can use recursion to repetitively reduce it to an elementary problem.

 

[shivajikobardan]

which college/university level math book could contain excerpts about recursive functions and practice problems?

 

[pbuk]

which college/university level math book could contain excerpts about recursive functions and practice problems?

Recursion in programming is associated with the mathematical concept of sequences but you won't find computing problems of this kind in a maths text book.

The Wikipedia article on this is quite a good start point https://en.wikipedia.org/wiki/Recursion_(computer_science)

 

[shivajikobardan]

Recursion in programming is associated with the mathematical concept of sequences but you won't find computing problems of this kind in a maths text book.

The Wikipedia article on this is quite a good start point https://en.wikipedia.org/wiki/Recursion_(computer_science)

that's like entire dsa(recursion related) in 1 post.

 

[FactChecker]

Now, I am wondering how it'll be for finding a palindrome of a number? I've a solution but I'm not understanding how we came towards it. I'm looking for how to come towards a solution than a solution itself.

It might help if you show the solution that you have questions about.

 

[shivajikobardan]

It might help if you show the solution that you have questions about.

solutions to this program are everywhere in internet.
https://www.studytonight.com/java-programs/java-program-to-check-palindrome-string-using-recursion

 

[FactChecker]

In that link, this is the critical part that hints at a solution using regression:
7. If the first and last characters of the string are the same then carry out the same for substring with the first and last character removed.

That means that the problem can be simplified to a smaller string to check for being a palindrome. Doing that over and over until the string is so short that it can be checked trivially.

 

[scottdave]

I had not heard of StudyTonight site before. Can anybody comment on it for learning (for example JavaScript)?

 

[pbuk]

Can anybody comment on it for learning (for example JavaScript)?

It seems completely useless for learning JavaScript. Stick to well known resources like Programiz.

 

[scottdave]

It seems completely useless for learning JavaScript. Stick to well known resources like Programiz.

Thanks