current community

your communities

more stack exchange communities

Stack Exchange
tour help
Take the 2-minute tour ×
Code Review Stack Exchange is a question and answer site for peer programmer code reviews. It's 100% free, no registration required.
up vote 0 down vote favorite

I've "solved" Project Euler Question 4 and I was wondering if I could make my answer more efficient (I'm using Project Euler to help me learn Haskell).

The problem reads:

Find the largest palindrome made from the product of two 3-digit numbers

Here is my solution

getMaxPalindrome = maximum[x*y | x<-[100..999], y<-[100..999], reverse(show(x*y)) ==show(x*y)]

All suggestions for improvement are appreciated!

share|improve this question

1 Answer 1

up vote 1 down vote accepted

First, since * is commutative, you can save 1/2 of your computation if you restrict yourself to cases where x >= y:

[ x*y | x<-[100..999], y<-[100..x], ... ]

Second, if you could generate all the products in a non-increasing list, you'd just be searching for the first element of such a list satisfying the predicate, which would also speed the search very much. See data-ordlist package, which implements many useful functions on sorted lists, in particular in your case you'll probably need unionBy or unionAllBy

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.