Posted by Michael Cooney on 12/15/06 06:31

Or you could use array_diff:

<?php

$list1 = "2,26,345";
$list2 = "3,4,26,35,525";

$alist1 = split(',', $list1);
$alist2 = split(',', $list2);

if(count(array_diff($alist1, $alist2)) == 0) {

echo "Yep. They're all in there.\n";

} else {

echo "Nope. Yer missing some.\n";
}

?>

Bob Stearns wrote:
> laredotornado@zipmail.com wrote:
> > Hi,
> >
> > I'm using PHP 4.4.4. Let's say I have two scalars, $list1 and $list2.
> > Both are comma separated lists of ordered, unsigned, unique integers.
> > An example would be
> >
> > $list1 = "2,26,345";
> > $list2 = "3,4,26,35,525";
> >
> > I am wondering if there is a short way of determining if all the
> > numbers in $list1 occur in $list2.
> >
> > Grateful for any advice. Thanks, - Dave
> >
> If, as in your example, the two lists are sorted, it can be done in
> O(n+m) time by doing stepped compare. If they are unsorted, it can also
> be done in O(n+m) time (with a much bigger constant factor) by making
> the second list into the subscripts of an array, then checking for the
> existence of the first list's elements in the new array.
>
> Sample code (untested):
>
> $i1 = 0;
> $i2 = 0;
> while($i1<count($list1) && $i2<count($list2)) {
> if($list2[$i2]==$list1[$i1]) {
> $i1++;
> $i2++;
> }
> elseif($list2[$i2]<$list1[$i1]) {
> $i2++;
> }
> else { /* this the failure case */ }
> $fail = TRUE;
> break;
> }
> }
>
> for($i2==0; $i2<count($list2); $i2++) {
> $test[$list2[$i2]] = TRUE;
> }
> for($i1==0; $i1<count($list1); $i1++) {
> if(!array_key_exists($list1[$i1],$test) {
> $fail = TRUE;
> break;
> }
> }
>
> We use these techniques rather than the much easier to code in_array()
> because the time for this technique in O(m*n) since $list2 must be
> searched completely for each element of $list1.

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