fix bug in filling histogram with pair cut

Author: ypwangg

PWGDQ/Tasks/dqEfficiency_withAssoc.cxx

@@ -2122,12 +2122,12 @@ struct AnalysisSameEventPairing {
               if (!(cut.IsSelected(VarManager::fgValues))) // apply pair cuts
                 continue;
               if (sign1 * sign2 < 0) {
-                fHistMan->FillHistClass(histNames[ncuts + icut * ncuts + iPairCut][0].Data(), VarManager::fgValues);
+                fHistMan->FillHistClass(histNames[ncuts + icut * PairCuts.size() + iPairCut][0].Data(), VarManager::fgValues);
               } else {
                 if (sign1 > 0) {
-                  fHistMan->FillHistClass(histNames[ncuts + icut * ncuts + iPairCut][1].Data(), VarManager::fgValues);
+                  fHistMan->FillHistClass(histNames[ncuts + icut * PairCuts.size() + iPairCut][1].Data(), VarManager::fgValues);
                 } else {
-                  fHistMan->FillHistClass(histNames[ncuts + icut * ncuts + iPairCut][2].Data(), VarManager::fgValues);
+                  fHistMan->FillHistClass(histNames[ncuts + icut * PairCuts.size() + iPairCut][2].Data(), VarManager::fgValues);
                 }
               }
             } // end loop (pair cuts)