순열 기반 코드 쉬운 구현

Permutation.java

List<List<Integer>> permute(List<Integer> input){
    List<List<Integer>> result = new ArrayList<>();
    permute(new ArrayList<>(), input, result);
    return result;
}

void permute(List<Integer> remain, List<Integer> input, List<List<Integer>> result){
    if(input.isEmpty()){
        result.add(remain);
        return;
    }
    else {
        for(int i=0; i<input.size(); i++){
            var temp = new ArrayList<Integer>(remain);
            temp.add(input.get(i));
            List<Integer> next = Stream.concat(input.subList(0, i).stream(), input.subList(i+1,input.size()).stream()).collect(Collectors.toList());
            permute(temp, next, result);
        }
    }
}