1|2|4|5
res: [ 1, 2,4,5, 3, 5, 6, 7, 12, 9, 11, 7 ]
fun (arr[], index, int sum) {
if(index == arr.length){
res.add(sum);
return;
}
sum = sum + arr.get(index) ;
fun(arr, index+1, sum )
sum = sum-arr.get(index) ;
fun(arr, index+1, sum);
}