An array of 2000 data entries to find the index with duplicate values

An array of 2000 data entries and an index with duplicate values. for example, an array contains ,............... the repeat indexes, 14 & nbsp; 5, 15 & nbsp ;.... it cannot be a two-for or while loop, which is too costly. ----- an array of 2000 data records, and an index with duplicate values is found.
For example, an array contains ,...............

Obtain 2 duplicate indexes, 2, 3, 10, 11, and 14.
5 duplicate indexes 7, 8, 15
....

It cannot be a two-for or while loop, which is too costly.

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PHP code

$ Arr = array (,); $ tmp = array (); foreach ($ arr AS $ k =>v v) {if (isset ($ tmp [$ v]) {if ($ tmp [$ v]) {$ tmp [$ v]. = "," ;}$ tmp [$ v]. = $ k;} else {$ tmp [$ v] = "" ;}} foreach ($ tmp AS $ k => $ v) {if ($ v) {echo $ k, "=>", $ v, "\ n" ;}} unset ($ tmp );
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PHP code
   
   
$ A = array (,); $ r = array (); foreach ($ a as $ v) {if (isset ($ r [$ v]) continue; if ($ t = array_keys (array_intersect ($ a, array ($ v )))) {unset ($ t [0]); $ r [$ v] = join (',', $ t) ;}$ r = array_diff ($ r, array (''); print_r ($ r );
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PHP code
     
     
$arr = array(1,2,2,2,3,4,5,5,5,6,2,2,7,8,2,5,3,9);$str = implode(',', $arr);foreach ($arr as $k=>$v){    $t[$v] .= !isset($t[$v]) ? '' : $k . ',';    $l += strlen($v);    if((strrpos($str, $v.'')) == $l-strlen($v))        $t[$v] = trim($t[$v], ',');    ++$l;}print_r($t);