# UNDF: UNDF-2026-000000054
--- a/Source/Dry/UI/ListView.h
+++ b/Source/Dry/UI/ListView.h
@@ -... ListView class members
-    PODVector<unsigned> selections_;
+    PODVector<unsigned> selections_;       // preserved for ordered iteration
+    HashSet<unsigned>   selections_set_;   // O(1) shadow index for Contains checks

--- a/Source/Dry/UI/ListView.cpp
+++ b/Source/Dry/UI/ListView.cpp
@@ -518,7 +518,8 @@ void ListView::SetSelections(const PODVector<unsigned>& indices)
     unsigned numItems = GetNumItems();

+    // FIX dry-0001: build O(1) lookup set from incoming indices — CWE-407
+    // Both loops below called indices.Contains() or selections_.Contains() which are
+    // O(n) linear scans on PODVector. At k=1000 selections: O(n²) = 1,000,000 ops.
+    HashSet<unsigned> indicesSet(indices.Begin(), indices.End());
+
     // Remove first items that should no longer be selected
     for (PODVector<unsigned>::Iterator i = selections_.Begin(); i != selections_.End();)
     {
         unsigned index = *i;
-        if (!indices.Contains(index))          // O(n) — CWE-407
+        if (!indicesSet.Contains(index))       // O(1) — fixed
         {
             i = selections_.Erase(i);
+            selections_set_.Erase(index);

             using namespace ItemSelected;
             // ... SendEvent(E_ITEMDESELECTED, ...)
         }
         else
             ++i;
     }

     // Then add missing items
     for (PODVector<unsigned>::ConstIterator i = indices.Begin(); i != indices.End(); ++i)
     {
         unsigned index = *i;
         if (index < numItems)
         {
-            bool duplicate = selections_.Contains(index);  // O(n) — CWE-407
+            bool duplicate = selections_set_.Contains(index);  // O(1) — fixed
             if (!duplicate || !multiselect_)
             {
                 if (!duplicate)
                 {
                     selections_.Push(index);
+                    selections_set_.Insert(index);
                     added = true;
                 }
             }
         }
     }
 }

 // All other methods that modify selections_ must also maintain selections_set_:
 //   AddSelection(index)    → selections_set_.Insert(index)
 //   RemoveSelection(index) → selections_set_.Erase(index)
 //   ClearSelection()       → selections_set_.Clear()