php实现‘浏览记录’按日期分组

出题：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，还是忍不住打出来，如下：

/* 简化版的函数 */
function groupVisit($visit)
{
    $visit_list = [];
    foreach ($visit as $v) {
        $visit_list[date('Y年m月d日', $v['visittime'])][] = $v;
    }
    return $visit_list;
}

好，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"
    }
  }
}

对的，这正是我想要的效果。

思考：java或C++等其他后台语言要怎么简洁地实现这个效果呢？用map库？python用dictionary？

-end-

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php实现‘浏览记录’按日期分组

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