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<?php function numberOfPairs($a, $k) { $cnt = 0; $used=[]; for($i=0; $i<count($a); $i++){ for($j=$i; $j<count($a); $j++){ if($a[$i]+$a[$j] == $k && !in_array($a[$i], $used) && !in_array($a[$i],$used)){ $arrRes[$i][0] = $a[$i]; $arrRes[$i][1] = $a[$j]; $used[] = $a[$i]; $used[] = $a[$j]; $used = array_unique($used); $cnt++; } } } sort($arrRes); //print $cnt; $d = $cnt; for($i=0; $i<count($arrRes); $i++){ for($j=0; $j<count($arrRes); $j++){ $diff = array_diff($arrRes[$i], $arrRes[$j]); if($diff == null) $d += 1; } } print $d; Var_dump($arrRes); } $a = [6,6,3,9,3,5,1]; $k = 12; numberOfPairs($a, $k);
Output for 5.6.0 - 5.6.40, 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 7.2.0 - 7.2.34, 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 - 8.2.19, 8.3.0 - 8.3.7
4array(2) { [0]=> array(2) { [0]=> int(3) [1]=> int(9) } [1]=> array(2) { [0]=> int(6) [1]=> int(6) } }

preferences:
239.71 ms | 404 KiB | 302 Q