[PWGDQ] Fix table reservation problem (#17230)

Co-authored-by: Jifeng Deng <jifeng.deng@cern.ch>
Co-authored-by: ALICE Action Bot <alibuild@cern.ch>

Author: 3 people

PWGDQ/Tasks/tableReader_withAssoc.cxx

@@ -3496,7 +3496,7 @@ struct AnalysisAsymmetricPairing {
 
   // Template function to run same event pairing with asymmetric pairs (e.g. kaon-pion)
   template <bool TTwoProngFitter, int TPairType, uint32_t TEventFillMap, uint32_t TTrackFillMap, typename TEvents, typename TTrackAssocs, typename TTracks>
-  void runAsymmetricPairing(TEvents const& events, Preslice<TTrackAssocs>& preslice, TTrackAssocs const& assocs, TTracks const& /*tracks*/)
+  void runAsymmetricPairing(TEvents const& events, Preslice<TTrackAssocs>& preslice, TTrackAssocs const& /*assocs*/, TTracks const& /*tracks*/)
   {
     fPairCount.clear();
 
@@ -3509,8 +3509,23 @@ struct AnalysisAsymmetricPairing {
 
     int sign1 = 0;
     int sign2 = 0;
-    ditrackList.reserve(assocs.size());
-    ditrackExtraList.reserve(assocs.size());
+
+    // Reserve capacity for the output tables
+    int64_t reserveSize = 0;
+    for (auto const& event : events) {
+      if (!event.isEventSelected_bit(0)) {
+        continue;
+      }
+      if (fConfigRemoveCollSplittingCandidates.value && event.isEventSelected_bit(2)) {
+        continue;
+      }
+      auto groupedLegAAssocs = legACandidateAssocs.sliceBy(preslice, event.globalIndex());
+      auto groupedLegBAssocs = legBCandidateAssocs.sliceBy(preslice, event.globalIndex());
+      reserveSize += static_cast<int64_t>(groupedLegAAssocs.size()) *
+                     static_cast<int64_t>(groupedLegBAssocs.size());
+    }
+    ditrackList.reserve(reserveSize);
+    ditrackExtraList.reserve(reserveSize);
 
     constexpr bool trackHasCov = ((TTrackFillMap & VarManager::ObjTypes::TrackCov) > 0 || (TTrackFillMap & VarManager::ObjTypes::ReducedTrackBarrelCov) > 0);