[SOLVED] Checking if all values are sequential, starting from 1 (or 0)

[448191]

Should be simple but I can't figure it out.

 

Say I have an array like so:

 

$pages = array(0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11);

 

or any other array with sequential values that starts with 0 (or 1, doesn't matter).

 

How do I assert that all values are indeed sequential, without looping through the values?

[AndyB]

If the array values are an arithmetic progression, then from count() and diff between consecutives you can determine the expected sum of all values. If it equals array_sum() then you have all values in the array.

[448191]

I figured as much, but didn't know how to calculate what the sum should be. I figured it out though:

 

<?php
$pages = array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

var_dump(
array_sum($pages) == (max($pages) + min($pages)) * (max($pages) / 2)
);

 

 

[AndyB]

FYI - http://library.thinkquest.org/20991/gather/formula/data/213.html works for all arithmetic progressions.