sorting hash map based on interger

Question

Trying to sort a list in descending order, so longest time first. This is my method I used few pages from here to make it correct however something in my code is wrong and it returns the list which is not so correct.

public static ArrayList<String> winnerIs(List<HP> hp){
        //System.out.println("1");
        int size = hp.size();
        //System.out.println(size);
        ArrayList<HP> listofWinner = new ArrayList<HP>();
        Map<String, Integer> map = new HashMap<String, Integer>();

        for(int i = 0; i < size; i++){
            listofWinner.add(hp.get(i));
            map.put(hp.get(i).getName(), hp.get(i).TD1());
            //System.out.println(hp.get(i).getName()+" "+hp.get(i).TD1());
        }
        //sort based on time
        ArrayList<String> keys = new ArrayList<String>(map.keySet());
        //System.out.println("---------------");
        /*for(int i = 0; i < keys.size(); i++){ 
            //wn.add(keys.get(i));
            System.out.println("here "+keys.get(i));
        }*/
        //System.out.println("---------------");


        ArrayList<String> wn = new ArrayList<String>();

        //System.out.println("---------------");
        for(int i = keys.size()-1; i >= 0; i--){    
            wn.add(keys.get(i));

        }
        return wn;
    }

here is what it reurns:

[team2, team1, team4, team3]

but it should be like this:

[team4, team3, team2, team1]

it doesn't matter if the time is equal, we just need the better time, I am not sure what part of the code is wrong.

even when I use this

ArrayList<Integer> s = new ArrayList<Integer>(map.values());
        Collections.sort(keys);
        //System.out.println("---------------");
        for(int i = 0; i < s.size(); i++){  
            //wn.add(keys.get(i));
            System.out.println("here "+s.get(i));
        }

the result are still not correct here is what it returns:

here 2
here 9
here 0
here 0

so I used one of the pages at stackoverflouw and I found this solution:

public static ArrayList<String> winnerIs(List<HumanPlayer> hp){
        //System.out.println("1");
        int size = hp.size();
        //System.out.println(size);
        ArrayList<HumanPlayer> listofWinner = new ArrayList<HumanPlayer>();
        Map<String, Integer> map = new HashMap<String, Integer>();

        for(int i = 0; i < size; i++){
            listofWinner.add(hp.get(i));
            map.put(hp.get(i).getName(), hp.get(i).getTimeDriver1());
            //System.out.println(hp.get(i).getName()+" "+hp.get(i).getTimeDriver1());
        }
        map.entrySet().stream()
        .sorted(Map.Entry.<String, Integer>comparingByValue().reversed()) 
        .limit(1000) 
        .forEach(System.out::println);

        return null;
    }

this returns the correct list but I am not sure what is this: .limit(1000) and also how can I equal this to a list, so I can return it.

Answer 1

Assuming the TD1() method in your HP class is the value you want to sort against, and that you really want to use a Map to help you sort. I think you want something like this

Map<Integer, List<String>> map = new HashMap<Integer, List<String>>();
for (HP h : hp) {
    if (map.get(h.TD1() != null) {
        map.get(h.TD1()).add(h.getName());
    }
    else {
      List temp = new ArrayList<String>();
      temp.add(h.getName());
      map.put(h.TD1(), temp);
    }
}
ArrayList keys = Arrays.asList(map.getKeyset().toArray());
Collections.sort(keys);

for ( int i = keys.length() - 1; i >= 0; i--) {
    List<String> names = map.get(i);
    // print names
}

Answer 2

You can use Java 8 for a nice sorting by value of the map:

Map<String, Integer> sorted = /* your map */.entrySet().stream()
        .sorted(Entry.comparingByValue()) //comparator for value, can reverse or use other
        .collect(Collectors.toMap(Entry::getKey, Entry::getValue,
                (e1, e2) -> { throw new IllegalArgumentException("Duplicate Key: " + e1.getKey()); },
                LinkedHashMap::new));

I chose to throw an exception for a duplicate key (the merging function, the 3rd argument of the Collectors#toMap), but you can also just return the first key found:

.collect(Collectors.toMap(Entry::getKey, Entry::getValue, (e1, e2) -> e1, LinkedHashMap::new));

The thing to keep in mind is the contracts that individual maps uphold. HashMap is an unsorted map and will not guaruntee iteration order (so sorting would be a fruitless endeavor), and a TreeMap is a SortedMap, but that contractually means it's sorted by key, not value. A LinkedHashMap will preserve iteration order, usually based on insertion (much like a List), and thus is usually what you want when you need to have a sorted map output.

Answer 3

Check this psuedo-code out, I believe you would get overall idea looking at this.

Map<Integer,List<String> map = new HashMap<Integer,List<String>>();
for(HP hpObject:hp) {
 if(map.containsKey(hpObject.TD1())) {
    map.get(hpObject.TD1()).add(hpObject.getName());
 } else {
    List<String> names = new ArrayList<String>();
    names.add(hpObject.getName());
    map.put(hpObject.TD1(),names);
 }
}

    // To sort by keys
    TreeMap sortedByTD = new TreeMap(map);

    // Iterate over TreeMap and create the list of winners you need
    return result;enter code here