http://www.synapsoft.co.kr/jsp/recruit/13_apply.html

azaa.php

<?php
function tests($expect, $actual) {
	if ($expect == $actual) {
		echo('PASS');
	} else {
		echo('FAIL');
	}

	echo(': ' . $expect . '/' . $actual . PHP_EOL);
}

function get_index($num) {
	$n = $num;
	$result = '';
	while ($n > 0) {
		$r = ($n % 26 == 0) ? 26 : $n % 26;
		$result = chr(65 + $r - 1) . $result;
		$n = ($n - $r) / 26;
	}

	return $result;
}

tests('A', get_index(1));
tests('B', get_index(2));
tests('O', get_index(15));
tests('T', get_index(20));
tests('Y', get_index(25));
tests('Z', get_index(26));
tests('AA', get_index(27));
tests('AB', get_index(28));
tests('ZZ', get_index(702));
tests('AAA', get_index(703));
tests('ACB', get_index(756));
tests('XFD', get_index(16384));
?>