比较对象数组元素的最佳方法

Question

So I have an array that consists of some number of objects that have both StartTime and Duration member variables. The startTime variable is a string in the format "14:20" and the Duration variable is a number, representing a number of minutes.

Can you guys recommend the best logic for going through the array and combining overlapping elements. For example, if the array had two objects, with the first one having a startTime of "00:00" & duration of 60 and the second object having a startTime of "08:00" & duration of 120 they would be left as separate elements BUT if the second object had a start time of "00:30" and a duration of 120, the two would be combined into one object with a startTime of "00:00" and a duration of 150.

I have been stuck on the general logic of this for some time, because I can't figure how to handle the case when two blocks are combined, but the new combined block creates a new overlap that must be handled. Am I just thinking about this wrong?! Usually I'm good with this sort of thing but am seriously struggling here.

Answer 1

expanding on @gavgrif...

i recommend something along these lines.

1. create new array field ['start'] in minutes from midnight (14:20 -> 188)
2. sort array by 'start' field
3. loop through array looking for overlapping items to merge into segments. where overlapping is that start of this new item is not greater than the segment end.

php example:

$segment  = array('start' => -1, 'end' => -1);  // force new segment on init
$segments = array();
foreach ($items as $item) {
    if ($item['start'] > $segment['end']) {

        // add current segment (ignore initial fake segment) to segments
        if ($segment['start'] > -1) {
            // close out current segment
            $segments[] = $segment;                
        }

        // start new segment
        $segment = $item;

    } else {

        // increment segment end if its later than current segment end
        $segment['end'] = max($segment['end'], $item['end'];
    }        
}

// close out final segment
$segments[] = $segment;

Answer 2

I would do this by creating two trees, one indexed by StartTime and the other indexed by EndTime (StartTime + Duration). Search both trees for elements that overlapped. Once the search was complete any found elements would be removed from both trees and the single new element (StartTime = minStartTime(searchResult), EndTime = maxEndTime(searchResult)) would be inserted into both trees.

Uses a little extra storage but I believe this makes your overlap problem trivial.

(Tree implementation left as an exercise :)