I'm trying to learn how to code and stumbled upon a problem generating a powerset of a source set in java. I try to write a method that returns a list of lists of doubles for a input of list of doubles. Sadly for a input of
[1.0, 2.0, 3.0]
it only returns
[[], [1.0], [1.0], [1.0, 2.0], [1.0], [1.0, 3.0], [1.0, 2.0], [1.0, 2.0, 3.0]]
so there has to be a matter with my for-loops. After hours of trying to find different ways of arranging the code, im stuck. Can someone spot the mistake i'm making for me? I would also appreciate some feedback on what I could improve on regarding usage of types/coding in general.
Thanks a lot!
Edit: had the wrong code in it
private static List<?> genSubset(List<Double> set, int size){
List<List<Double>> subsets = new ArrayList<List<Double>>();
System.out.println(set);
for (int x=0; x<Math.pow(2,size); x++)
{
List<Double> currentSet = new ArrayList<Double>();
for (int i = 0; i<size; i++){
try {if (Integer.toBinaryString(x).charAt(i)=='1'){
currentSet.add(set.get(i));
}
}
catch (Exception e){}
}
subsets.add(currentSet);
}
return subsets;
}
You are not considering that the indexing of a string is counted from the left side. You need to subtract i from the last index of the binary string. Fix to your code is as follows.
private static List<?> genSubset(List<Double> set, int size) {
List<List<Double>> subsets = new ArrayList<List<Double>>();
for (int x = 0; x < Math.pow(2, size); x++) {
List<Double> currentSet = new ArrayList<Double>();
String binString = Integer.toBinaryString(x);
for (int i = 0; i < size; i++) {
if (binString.length() > i && binString.charAt(binString.length()-i-1) == '1') {
currentSet.add(set.get(i));
}
}
subsets.add(currentSet);
}
return subsets;
}