如何检查PHP中多个日期范围之间的重叠？

<?php

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

function checkIfOverlapped($ranges)
{
    $res = $ranges[0];

    $countRanges = count($ranges);

    for ($i = 1; $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
$ranges = array(
    array('start' => '2014-01-01','end' => '2014-01-05'),array('start' => '2014-01-05','end' => '2014-01-10'),array('start' => '2014-01-04','end' => '2014-01-07')
);

var_dump(checkIfOverlapped($ranges));