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<?php $arr = ["a", "b", "a", "c"]; function makeUnique($arr){ $set = []; foreach($arr as $k => $v){ $set[ $v ] = ($set[ $v ] ?? 0) + 1; $arr[ $k ] = $arr[ $k ] . ($set[ $v ] > 1 ? '.' .($set[ $v ] - 1) : ''); } return $arr; } print_r(makeUnique($arr));

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