The 4th problem in Project Euler is this:
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.
The solution of Joseph looked like this:
He states that this code needs 22 seconds to execute. Wow, 22 seconds. This is a lot. Especially when compared to Python. Joseph writes that the Python version takes 0.33 seconds to execute.
One reason for Swift being that slow is that the initialization of strings is quite expensive. Swift strings are very complicated. Another reason is that Joseph presumably compiled without any optimization. So let’s see what happens when we fix both problems.
First let’s get rid of the String creation. This is a solution without strings:
I have added code to measure the execution time. Without any optimization I get an execution time of 0.84 seconds on my MacBook Air. With an optimization of Fast [-O] the execution time goes down to 0.42 seconds.
I think there is still room for improvement in the algorithm but 0.42 is already way better than 22.