Any ideas to make my code efficient for looping 10 000 000 000 times

Kevin Helma :

I've made a simple code to count the occurrences of the digit '14' from a given number. I've successfully print out the counter if the given number is 10 000 000 and it took less than 1 second. When i increase the number to 10 000 000 000 it took 459 seconds. Any ideas on how to make it runs faster?

long startTime = System.nanoTime();
        long counter = 0L;
        for (long i = 14; i <= 10000000000L; i++)
        {
            String s = Long.toString(i);//i.ToString();
            if (s.contains("14"))
            {
                counter += 1;
            }

        }
        long endTime   = System.nanoTime();
        long totalTime = endTime - startTime;
        long convert = TimeUnit.SECONDS.convert(totalTime, TimeUnit.NANOSECONDS);

        System.out.println(convert + " seconds");
        System.out.println(counter);

time taken : 459 seconds
number of 14 appears : 872348501

Andy Turner :

The most obvious optimization: don't construct strings.

Just check the last two digits of the number, and then divide by 10 until you find a 14:

boolean matches = false;
for (long num = i; num >= 14 && !matches; num /= 10) {
  matches = (num % 100) == 14;
}
if (matches) {
  counter += 1;
}

But, you would likely just be able to calculate the number of cases, using the inclusion/exclusion principle.