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<?php define("EOL", "\n"); $max = 40; $start = ord("a"); $limit = ord("y"); $arr = array(); $arr[0] = chr($start); while($max--){ for($i = 0; $i <= (count($arr) - 1); $i++){ if(ord($arr[$i]) > $limit){ $arr[$i] = chr($start); if(isset($arr[$i + 1])){ $arr[$i+1] = chr(ord($arr[$i+1]) + 1); } else { $arr[$i+1] = chr($start); } } } echo "[", implode("][", array_reverse($arr)), "]", EOL; $arr[0]++; }
Output for 5.5.0 - 5.5.38, 5.6.0 - 5.6.40, 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 7.2.0 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
[a] [b] [c] [d] [e] [f] [g] [h] [i] [j] [k] [l] [m] [n] [o] [p] [q] [r] [s] [t] [u] [v] [w] [x] [y] [a][a] [a][b] [a][c] [a][d] [a][e] [a][f] [a][g] [a][h] [a][i] [a][j] [a][k] [a][l] [a][m] [a][n] [a][o]

preferences:
248.92 ms | 404 KiB | 330 Q