Project Euler problem number 4 asks the following:
A palindromic number reads the same both ways. The largest palindrome made from the product of two 2-digit numbers is 9009 = 91 × 99.
Find the largest palindrome made from the product of two 3-digit numbers.
Here follows my solution:
A few considerations:
- I first define a general recursive function to determine whether a given string is a palindrome.
I basically check the first and last characters of the string; if they are the same I continue with the second and second last, and so on until I either found a pair of chars that do not match or there's only one char or none left.
Alternatively, I could have reversed the string and compared the original and reversed strings for equality; however that would have been not just more work than actually needed by the algorithm, but less useful as an excercise in learning F#.
- The actual algorithm uses brute force to test for palindromicity (neologism?) all the numbers that can be composed multiplying together 3 digits numbers (those from 100 to 999), picking the highest one. Again, as in a previous problem, I am using comprehension to generate a list of candidates.