S = { 1 ; 2; 3}
PowerSet = { 0 ; 1 ; 2; {1;2} ; 3; {1;3} ; {2;3} ; { 1;2;3} }

I need to put the elements of PowerSet as Key in HashMap so I can track some DP issue down
Option1: Make an array OR arrayList and put it down
Option2: String representation of an arrayList and put it down

Have people run into these issues before ? Any suggestions ?