检查日期范围（开始和结束日期）是否有重叠

Question

function checkDateOverlap($ranges) {
    $res = $ranges[0];
    $countRanges = count($ranges);

    for ($i = 0; $i < $countRanges; $i++) {

        $r1s = $res['start'];
        $r1e = $res['end'];

        $r2s = $ranges[$i]['start'];
        $r2e = $ranges[$i]['end'];

        if ($r1s >= $r2s && $r1s <= $r2e || $r1e >= $r2s && $r1e <= $r2e || $r2s >= $r1s && $r2s <= $r1e || $r2e >= $r1s && $r2e <= $r1e) {
            $res = array(
                'start' => $r1s > $r2s ? $r1s : $r2s,
                'end' => $r1e < $r2e ? $r1e : $r2e
            );
        } else 
            return false;
    }
    return $res;
}
// example of returned dates that overlap
$ranges = array(
    array('start' => '2014-01-01', 'end' => '2014-01-04'),
    array('start' => '2014-01-05', 'end' => '2014-01-10'),
    array('start' => '2014-01-04', 'end' => '2014-01-07')
);
//example of failure
$ranges2 = array(
        array('start' => '2014-01-01', 'end' => '2014-01-04'),
        array('start' => '2014-01-05', 'end' => '2014-01-10'),
        array('start' => '2014-01-11', 'end' => '2014-01-17')
    );

var_dump(checkDateOverlap($ranges));

The following is what I was attempting to check intersection of date ranges. In the array "ranges1" this example has overlapping dates. It should return the dates. In array $ranges2, this should pass as no intersecting dates.

Now the weird thing is the start and end date can be the exact same, so you could make an entry for just a single day. I've tried many things, and I'm stumped.

I believe there needs to be another for loop, but regardless I am not getting success.

Here was another go I had:

<?php

// pass your ranges to this method and if there is a common intersecion it will // return it or false

function checkDateOverlap($ranges){
    $res = $ranges[0];
    $countRanges = count($ranges);
    for ($i = 0; $i < count($countRanges); $i++) {
        for($j = $i+1; $j < count($countRanges); $j++) {
            $r1s = $res['start'];
            $r1e = $res['end'];

            $r2s = $ranges[$i]['start'];
            $r2e = $ranges[$i]['end'];

            if (($r1s >= $r2e && $r2s <= $r1e)) {

                $res[] = array(
                    'start' => $r1s > $r2s ? $r1s : $r2s,
                    'end' => $r1e < $r2e ? $r1e : $r2e
                );

            } else 
                return false;
        }
    }
    return $res;
}

// example
$ranges = array(
    array('start' => '2014-01-04', 'end' => '2014-01-05'),
    array('start' => '2014-01-06', 'end' => '2014-01-10'),
    array('start' => '2014-01-11', 'end' => '2014-01-13')
);

echo "<pre>";

var_dump(checkDateOverlap($ranges));
echo "</pre>";  

Any advice greatly appreciated.

Answer 1

$ranges = array(
        array('start' => new DateTime('2014-01-01'), 'end' => new DateTime('2014-01-05')),
        array('start' => new DateTime('2014-01-06'), 'end' => new DateTime('2014-01-06')),
        array('start' => new DateTime('2014-01-07'), 'end' => new DateTime('2014-01-07')),
    );

    function intersects($lhs, $rhs) {
        // Note that this function allows ranges that "touch", 
        // eg. one pair starts at the exact same time that the other ends.
        // Adding less "or equal to" will allow same start date 
        return !($lhs['start'] > $rhs['end'] || $lhs['end'] < $rhs['start']);
    }

    function checkDates($ranges) {
        // Comparison loop is of size n•log(n), not doing any redundant comparisons
        for($i = 0; $i < sizeof($ranges); $i++) {
            for($j = $i+1; $j < sizeof($ranges); $j++) {
                if(intersects($ranges[$i], $ranges[$j])) {
                    echo "Date {$i} intersects with date {$j}\n";
                }
            }
        }
    }

    checkDates($ranges);

I've attached my working code sample to hopefully help someone else in the future looking for the same solution. This will print the arrays that intersect.

Answer 2

If you use usort to first sort the dates, the work gets a lot easier. The following can be optimized a lot, but it is done step-by-step make it easier to understand.

//The date comparison function, sort on start and then on end
function cmp($a, $b)
{
    if($a['start']<$b['start']) return -1;
    if($a['start']>$b['start']) return 1;
    if($a['end']<$b['end']) return -1;
    if($a['end']>$b['end']) return 1;
    return 0; // start=start and end=end
}

$ranges = array(
    array('start' => '2014-01-01', 'end' => '2014-01-04'),
    array('start' => '2014-01-05', 'end' => '2014-01-10'),
    array('start' => '2014-01-04', 'end' => '2014-01-07')
);

usort($ranges, 'cmp'); // Sort the dates

$output = array();
for($i=0; $i<sizeof($ranges); $i++)
{
    $endindex = $i; // The index containing the proper 'end' value
    for($j=$i+1; $j<sizeof($ranges); $j++)
    {
        if($ranges[$endindex]['start'] == $ranges[$j]['start']) // Overlap
            $endindex = $j;
        elseif($ranges[$endindex]['end']>=$ranges[$j]['start']) // Overlap
            $endindex = $j;
    }
    $output[] = array('start' => $ranges[$i]['start'], 'end' => $ranges[$endindex]['end']);
    // Break the rules by hard-setting $i from the for loop - it works great in this case
    $i = $endindex;
}

print_r($output);

It works for your example. If you have other rules that must be used, hopefully you can adjust this code.

Answer 3

Here are some remarks:
- You do not check the validity of the date formed by 'start' and 'end'.
- Why do you not convert the dates to timestamp ?
-> It's more easier and faster to compare integer value instead of string ?

Why do you not use PHP DateTime and DateInterval Objects ?
http://php.net/manual/en/book.datetime.php