Overlapping date range peak

[Berre]

I need some help with creating this algorithm. The goal is to find the highest occurrence of overlapping date ranges.

 

Let's say I have some date ranges:

2012-02-21 - 2012-02-24

2012-02-21 - 2012-02-26

2012-02-23 - 2012-02-29

2012-02-24 - 2012-02-27

2012-02-26 - 2012-02-28

 

Of these the date 2012-02-24 and 2012-02-26 are overlapping 4 times, which is the highest number of overlapping dates. This number (4) is what I want to get. I don't care when the peak is, or how often it peaks, just the highest number of overlapping dates.

 

It's not important with a lot of exact PHP (you don't have to write the entire thing), but I'm completely lost for a simple and fast way of solving this.

[PFMaBiSmAd]

In order to find the maximum sum, you would need to iterate over each range of dates and maintain a sum for each date, then simply find the maximum.

 

<?php
$data[] = array('2012-02-21','2012-02-24');
$data[] = array('2012-02-21','2012-02-26');
$data[] = array('2012-02-23','2012-02-29');
$data[] = array('2012-02-24','2012-02-27');
$data[] = array('2012-02-26','2012-02-28');

$arr = array();
foreach($data as $range){
while($range[0] <= $range[1]){
	$arr[$range[0]] = isset($arr[$range[0]]) ? $arr[$range[0]] + 1 :1;
	$range[0] = date('Y-m-d',strtotime($range[0] . '+ 1 day'));
}
}

arsort($arr);
$peak = current($arr);
echo "Peak: $peak";