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javaalgorithmuniquecombinations

Generate all unique combinations of Items

I trying to generate all possible unique combination of items.

Ex: item1, item2, item3

Combinations: 
   item1+item2+item3
   item1+item2
   item1+item3
   item2+item3
   item1
   item2
   item3

I am unable to get an idea on how to solve this?

for(int i=0;i<size;i++){
   for(int j=i+1;j<size;j++){
       System.out.println(list.item(i)+list.item(j));
   }
}

The above code certainly works for all unique combination of two elements. But not for 3 element pair and more..

Solution

  • If you have N items, count from 1 to 2^N-1. Each number represents a combination, like so: if bit 0 (the least significant bit) is set, item1 is in the combination. If bit 1 is set, item2 is in the combination, and so on.

    If you don't want 1-item combinations, start counting at 3, and ignore all the combinations that are a power of 2 (4, 8, 16, etc...).