Error in OrdDenseSet implementation

Using `OrdDenseSet` in the partitioner yields the following result:
```
./build/algorithms/partitioner/sbg-partitioner -f ./test/partitioner/air_conditioners_1000.json -p 4
filename is ./test/partitioner/air_conditioners_1000.json
number of partitions is 4
sb_graph: V: {[0:999], [1000:1999], [2000:2999], [3000:3999]}
Vmap: <<>>

E: {[4000:4999], [5000:5999], [6000:6999], [7000:7999]}
map1: <<{[4000:4999]} -> x-3000, {[5000:5999]} -> x-2000, {[6000:6999]} -> x-6000, {[7000:7999]} -> x-5000>>
map2: <<{[4000:4999]} -> x-4000, {[5000:6999]} -> x-5000, {[7000:7999]} -> x-6000>>
Emap: <<>>
subEmap: <<>>
node weight = << >>
edge costs = << >>

aux_rmap: <<{[1000:1999], [1000:1999]} -> x-1000, {[3000:3999], [3000:3999]} -> x-3000, {[0:999], [0:999], [0:999], [0:999], [0:999], [0:999], [0:999], [0:999], [0:999], [0:999], [0:999], [0:999]} -> x+1000, {[2000:2999], [2000:2999]} -> x-1000, {[0:999], [0:999], [0:999], [0:999], [0:999], [0:999], [0:999], [0:999], [0:999], [0:999], [0:999], [0:999], [1000:1999], [1000:1999], [2000:2999], [2000:2999], [3000:3999], [3000:3999]} -> x, {[1000:1999], [1000:1999]} -> x-1000, {[0:999], [0:999]} -> x+1000, {[0:999], [0:999]} -> x+3000, {[0:999], [0:999]} -> x+3000, {[0:999], [0:999]} -> x+1000, {[0:999], [0:999], [1000:1999], [1000:1999], [2000:2999], [2000:2999], [3000:3999], [3000:3999]} -> x>>
```