[PWGEM/Dilepton] fix duplicated pairs in studyDCAFitter.cxx (#16605)

Author: dsekihat

PWGEM/Dilepton/Tasks/studyDCAFitter.cxx

@@ -858,25 +858,19 @@ struct studyDCAFitter {
         } // end of electron loop
       } // end of positron loop
 
-      for (const auto& posId1 : positronIds) {
-        auto pos1 = tracks.rawIteratorAt(posId1);
-        for (const auto& posId2 : positronIds) {
-          auto pos2 = tracks.rawIteratorAt(posId2);
-          if (pos1.globalIndex() == pos2.globalIndex()) {
-            continue;
-          }
+      for (size_t i = 0; i < positronIds.size(); i++) {
+        auto pos1 = tracks.rawIteratorAt(positronIds[i]);
+        for (size_t j = i + 1; j < positronIds.size(); j++) {
+          auto pos2 = tracks.rawIteratorAt(positronIds[j]);
           runSVFinder<1>(collision, pos1, pos2, mcParticles);
           runPairingAtPV<1>(pos1, pos2, mcParticles);
         } // end of positron loop
       } // end of positron loop
 
-      for (const auto& eleId1 : electronIds) {
-        auto ele1 = tracks.rawIteratorAt(eleId1);
-        for (const auto& eleId2 : electronIds) {
-          auto ele2 = tracks.rawIteratorAt(eleId2);
-          if (ele1.globalIndex() == ele2.globalIndex()) {
-            continue;
-          }
+      for (size_t i = 0; i < electronIds.size(); i++) {
+        auto ele1 = tracks.rawIteratorAt(electronIds[i]);
+        for (size_t j = i + 1; j < electronIds.size(); j++) {
+          auto ele2 = tracks.rawIteratorAt(electronIds[j]);
           runSVFinder<2>(collision, ele1, ele2, mcParticles);
           runPairingAtPV<2>(ele1, ele2, mcParticles);
         } // end of electron loop