<?php
$mass       = array(
    10,
    20,
    100,
    30,
    40,
    104,
    200,
    202,
    33
);
$lastValue1 = $mass[0];
$lastValue2 = $mass[1];
$lastDef    = abs($mass[0] - $mass[1]);
$k          = 1;
 
for ($i = 1; $i < count($mass); $i++) {
    $k = 0;
    do {
 
        $def = abs($mass[$k] - $mass[$i]);
 
        if ($def == 0) {
            continue;
        }
        if ($def < $lastDef) {
            $lastDef    = $def;
            $lastValue2 = $mass[$k];
            $lastValue1 = $mass[$i];
        }
        $k++;
    } while ($k < $i);
 
}
echo "$lastValue1<br>";
echo "$lastValue2<br>";

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