finding common prefix of array of strings

Question

I have an array like this:

$sports = array(
\'Softball - Counties\',
\'Softball - Eastern\',
\'Softball - North Harbour\',
\'Softball - South\',
\'Softball -         


        

Answer 1

I would use this:

$prefix = array_shift($array);  // take the first item as initial prefix
$length = strlen($prefix);
// compare the current prefix with the prefix of the same length of the other items
foreach ($array as $item) {
    // check if there is a match; if not, decrease the prefix by one character at a time
    while ($length && substr($item, 0, $length) !== $prefix) {
        $length--;
        $prefix = substr($prefix, 0, -1);
    }
    if (!$length) {
        break;
    }
}

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Update   Here’s another solution, iteratively comparing each n-th character of the strings until a mismatch is found:

$pl = 0; // common prefix length
$n = count($array);
$l = strlen($array[0]);
while ($pl < $l) {
    $c = $array[0][$pl];
    for ($i=1; $i<$n; $i++) {
        if ($array[$i][$pl] !== $c) break 2;
    }
    $pl++;
}
$prefix = substr($array[0], 0, $pl);

This is even more efficient as there are only at most numberOfStrings‍·‍commonPrefixLength atomic comparisons.