PHP 实现浏览记录并按日期分组

现有测试数据如下，要求实现如下图中的效果：

array(4) { [0] => array(6) { ["visit_id"] => int(127) ["goods_id"] => int(16) ["visittime"] => int(1494399935) ["goods_name"] => string(53) "OPPO R9s 全网通4G+64G 双卡双待手机 玫瑰金" ["shop_price"] => string(6) "500.00" } [1] => array(6) { ["visit_id"] => int(124) ["goods_id"] => int(13) ["visittime"] => int(1494399921) ["goods_name"] => string(76) "SIEMENS/西门子 KA92NV09TI双开门家用对开门电冰箱变频旗舰款" ["shop_price"] => string(7) "4000.00" } [2] => array(6) { ["visit_id"] => int(123) ["goods_id"] => int(27) ["visittime"] => int(1494399903) ["goods_name"] => string(85) "爱他美白金版Aptamil 幼儿配方奶粉3段(12-36个月适用)900g(欧洲进口)" ["shop_price"] => string(6) "329.00" } [3] => array(6) { ["visit_id"] => int(120) ["goods_id"] => int(26) ["visittime"] => int(1494224263) ["goods_name"] => string(21) "欢乐谷免票一张" ["shop_price"] => string(5) "50.00" }}

还没实现之前我想这个代码不知道要O(n)呢还是更高的复杂度才能实现，细想一下，其实php的数组底层就是哈希实现的，如何简单利用这个特性使复杂度降到O(1)呢？

show me the code：

/* 浏览记录按日期分组 */function groupVisit($visit){ $curyear = date('Y'); $visit_list = []; foreach ($visit as $v) {  if ($curyear == date('Y', $v['visittime'])) {   $date = date('m月d日', $v['visittime']);  } else {   $date = date('Y年m月d日', $v['visittime']);  }  $visit_list[$date][] = $v; } return $visit_list;}

说明：入参 $visit 就是上面一开始的测试数据，函数中还对用户体验做了一些优化，比如，你的浏览记录中总是显示出今年的年份，是不是感觉有点冗余，所以如果是本年份的话，年份就要隐藏起来，其他年份还是照样显示出来。不然代码会更加简洁。

好了上面的测试数据经过该函数之后，再把返回值打印出来，有：

array(2) { ["05月10日"] => array(3) { [0] => array(6) {  ["visit_id"] => int(127)  ["goods_id"] => int(16)  ["visittime"] => int(1494399935)  ["goods_name"] => string(53) "OPPO R9s 全网通4G+64G 双卡双待手机 玫瑰金"  ["shop_price"] => string(6) "500.00" } [1] => array(6) {  ["visit_id"] => int(124)  ["goods_id"] => int(13)  ["visittime"] => int(1494399921)  ["goods_name"] => string(76) "SIEMENS/西门子 KA92NV09TI双开门家用对开门电冰箱变频旗舰款"  ["shop_price"] => string(7) "4000.00" } [2] => array(6) {  ["visit_id"] => int(123)  ["goods_id"] => int(27)  ["visittime"] => int(1494399903)  ["goods_name"] => string(85) "爱他美白金版Aptamil 幼儿配方奶粉3段(12-36个月适用)900g(欧洲进口)"  ["shop_price"] => string(6) "329.00" } } ["05月08日"] => array(1) { [0] => array(6) {  ["visit_id"] => int(120)  ["goods_id"] => int(26)  ["visittime"] => int(1494224263)  ["goods_name"] => string(21) "欢乐谷免票一张"  ["shop_price"] => string(5) "50.00" } }}