Optimization (in terms of speed ) of hashmap for large Arraylist-CodePudding

This code takes O(n) time and O(n) space is there any other way to optimize this code. I was thinking about the multithread. Anyone can come up with better way because this is taking lot of time in main code. Thanks alot;)

String[] nums = {"A","C","trump tower","hmm's","CAP","C","hmm","trump Tower"};
    HashMap<String, Integer> hmap = new HashMap<String, Integer>();
    List<String> dup = new ArrayList<String>();
    List<String> nondup = new ArrayList<String>();
    for (String num : nums) {
        String x= num;
        String result = x.toLowerCase();
        if (hmap.containsKey(result)) {
            hmap.put(result, hmap.get(result)   1);
        }
        else {
            hmap.put(result,1);
        }
    }
    for(String num:nums){
        int count= hmap.get(num.toLowerCase());
        if (count == 1){
            nondup.add(num);
        }
        else{
            dup.add(num);
        }
    }

Output: Dup- [C, trump tower, C, trump Tower] nonDup- [A, hmm's, CAP, hmm]

CodePudding user response：

How much time is "a lot of time"? Is your input bigger than what you've actually shown us?

You could parallelize this with something like Arrays.parallelStream(nums).collect(Collectors.groupingByConcurrent(k -> k, Collectors.counting()), which would get you a Map<String, Long>, but that would only speed up your code if you have a lot of input, which it doesn't look like you have right now.

You could parallelize the next step, if you liked, like so:

Map<String, Long> counts = Arrays.parallelStream(nums)
   .collect(Collectors.groupingByConcurrent(k -> k, Collectors.counting());
Map<Boolean, List<String>> hasDup =
   counts.entrySet().parallelStream()
     .collect(Collectors.partitioningBy(
        entry -> entry.getValue() > 1,
        Collectors.mapping(Entry::getKey, Collectors.toList())));

List<String> dup = hasDup.get(true);
List<String> nodup = hasDup.get(false);

CodePudding user response：

Set<String> hash_Set = new HashSet<String>();
    List<String> dup = new ArrayList<String>();
    List<String> nondup = new ArrayList<String>();
    for(String num:nums)
    {
            if(hash_Set.add(num)){
                    nondup.add(num);
            }
            else{
                dup.add(num);
            }
     }