feat(problemset): move hardness filter to right side and improve UX

- Relocate hardness dropdown from left to right side of filter controls
- Change form submission behavior to update URL parameters directly
- Preserve selected hardness value on page reload
- Remove page parameter when hardness changes to reset pagination
- Improve visual alignment and spacing in filter interface

web/template/syzoj/problemset.php

@@ -17,26 +17,6 @@
               <div class="results" style="width: 100%; "></div>
             </div>
 
-            <div class="ui selection dropdown" style="width: 120px; height: 28px; margin-top: -5.3px; float:left; margin-right: 10px;">
-              <input type="hidden" name="hardness" value="<?php
-              $selected_hardness = 0;
-              if (isset($_GET['hardness'])) {
-                $selected_hardness = intval($_GET['hardness']);
-                if ($selected_hardness < 1 || $selected_hardness > 8)
-                  $selected_hardness = 0;
-              }
-              echo $selected_hardness;
-              ?>">
-              <i class="dropdown icon"></i>
-              <div class="default text">难度</div>
-              <div class="menu">
-                <div class="item" data-value="0">全部难度</div>
-                <?php for ($h = 1; $h <= 8; $h++) {
-                  echo '<div class="item" data-value="' . $h . '">难度 ' . $h . '</div>';
-                } ?>
-              </div>
-            </div>
-
           <?php if (isset($_SESSION[$OJ_NAME . '_' . 'administrator'])): ?>
             <div class="ui search" style="width: 120px; height: 28px; margin-top: -5.3px; display: inline-block;">
               <div class="ui icon input" style="width: 100%; ">
@@ -119,23 +99,48 @@
           </script>
           <label>显示已正确题目</label>
         </div>
-        <div style="margin-left: 10px; display: inline-block; ">
-          <a style="margin-left: 10px; " href="category.php" class="ui labeled icon mini green button"><i
-              class="plus icon"></i> <?php echo $MSG_SHOW_ALL_TAGS; ?></a>
 
+        <?php
+        $selected_hardness = 0;
+        if (isset($_GET['hardness'])) {
+          $selected_hardness = intval($_GET['hardness']);
+          if ($selected_hardness < 1 || $selected_hardness > 8)
+            $selected_hardness = 0;
+        }
+        ?>
+        <div class="ui selection dropdown" id="hardness_dropdown" style="width: 120px; height: 28px; margin-left: 10px; vertical-align: middle;">
+          <input type="hidden" id="hardness_value" value="<?php echo $selected_hardness; ?>">
+          <i class="dropdown icon"></i>
+          <div class="default text">难度</div>
+          <div class="menu">
+            <div class="item" data-value="0">全部难度</div>
+            <?php for ($h = 1; $h <= 8; $h++) {
+              echo '<div class="item" data-value="' . $h . '">难度 ' . $h . '</div>';
+            } ?>
+          </div>
         </div>
-
       </div>
     </div>
   </div>
 
   <script>
     $(function () {
-      $('.ui.dropdown').dropdown({
+      $('#hardness_dropdown').dropdown({
-        onChange: function () {
+        onChange: function (value) {
-          $(this).closest('form').submit();
+          var params = new URLSearchParams(window.location.search);
+          if (value == '0' || value === '') {
+            params.delete('hardness');
+          } else {
+            params.set('hardness', value);
+          }
+          params.delete('page');
+          window.location.href = '?' + params.toString();
         }
       });
+      var hv = $('#hardness_value').val();
+      if (hv && hv !== '0') {
+        $('#hardness_dropdown').dropdown('set selected', hv);
+      }
     });
   </script>