Question

I have an ArrayList of elements with a timestamp.

Given an element of this array, I would like to select all the elements happing a certain time before and after that given element.

The problem is that this time stamp goes to 60 000 milisec and then start again from zero.

So if I would like to get all the elements happening, say 1000 milisec before and after the element with timestamp 59 999 I don’t know how to do this.

I have been looking at the modulus operation but I don’t seem able to make it work.

Answer 1

Try this:

List<Integer> timestamps;
int target = 59999; // matches are from 58999 to 999 (wrapped around)
for (Integer timestamp : timestamps) {
    if (Math.abs(timestamp + 60000 - target) <= 1000 || Math.abs(timestamp - target) <= 1000) {
        // this timestamp is a match
    }
}

This code simply check twice – once each for roll-over and non-roll-over.

I’ve tested it and it works for “roll-under” as well – ie when the target is less than 1000 (so the range would be between 59000 + target and target)