从 java 的列表中查找（减少）列表的适当子集

Question

I want to get something like this below:

//Input:
{
    "paths": [
        [
            "A","B"
        ],
        [
            "A","B","C"
        ],
        [
            "A","C"
        ],
        [
            "A","D"
        ],
        [
            "A"
        ]
    ]
}

//Output:
{
    "paths": [
        
        [
            "A","B","C"
        ],
        [
            "A","D"
        ]
       
    ]
}

What my code looks like:

List<LinkedList<String>> paths = new LinkedList<>();
//...
//some process that adds elements to paths.

paths.sort(Comparator.comparingInt(LinkedList::size));

List<LinkedList<String>> uniquePaths = new ArrayList<>();

                for (int i = 0; i < paths.size(); i++) {
                    boolean unique=true;
                    for (int j = i+1 ; j < paths.size(); j++) {

                        if (paths.get(j).containsAll(paths.get(i))){
                            unique=false;
                            break;
                        }
                    }
                    if(unique) {
                        uniquePaths.add(paths.get(i));
                    }
                }

But this logic seems a bit off.(This is resulting in something like: [[A][A,D][A,B,C]] ) Please help with some better way of solving this.

Similar Question but in R: How to reduce (subset) list of lists?

Answer 1

You're not checking each combination against the whole data set. Your mistake is rooted in the nested loop, where iteration starts from the index j=i+1 .

Since performance of the containsAll() depends on the collection that is passed as an argument, it makes sense to generate a List of Sets out of the given list of list.

Here's how it can be implemented using Stream API.

List<List<String>> source = List.of(
    List.of("A", "B"), List.of("A", "B", "C"),
    List.of("A", "C"), List.of("A", "D"), List.of("A")
);
        
List<Set<String>> sets = source.stream()
    .map(HashSet::new)
    .collect(Collectors.toList());
    
List<List<String>> result = sets.stream()
    .filter(set -> sets.stream().filter(s -> !s.equals(set)).noneMatch(s -> s.containsAll(set)))
    .map(ArrayList::new)
    .collect(Collectors.toList());
    
System.out.println(result);

Output:

[[A, B, C], [A, D]]

Note that we need to exclude the current combination of strings while checking whether it is a subset of any of the other elements or not, see filter(s ->.s.equals(set)) in the code above.