Get the highest values in a hashmap in java

Question

I have a HashMap which contains the following values:

Map<String, Integer> map = new HashMap<>();
map.put("name1", 3);
map.put("name2", 14);
map.put("name3", 4);
map.put("name4", 14);
map.put("name5", 2);
map.put("name6", 6);

How do I get all keys with the highest value? So that I get the following keys in this example:

name2
name4

Solution 1

The first step is to find the highest value at all.

int max = Collections.max(map.values());

Now iterate through all the entries of the map and add to the list keys associated with the highest value.

List<String> keys = new ArrayList<>();
for (Entry<String, Integer> entry : map.entrySet()) {
    if (entry.getValue()==max) {
        keys.add(entry.getKey());
    }
}

If you like the Java 8 Stream API, try the following:

map.entrySet().stream()
    .filter(entry -> entry.getValue() == max)
    .map(entry -> entry.getKey())
    .collect(Collectors.toList());

Solution 2

The response from Nikolas Charalambidis is quite neat, but it may be faster to do it in just one step (iteration), supposing that the input map was much larger:

public static List<String> getKeysWithMaxValue(Map<String, Integer> map){
    final List<String> resultList = new ArrayList<String>();
    int currentMaxValuevalue = Integer.MIN_VALUE;
    for (Map.Entry<String, Integer> entry : map.entrySet()){
        if (entry.getValue() > currentMaxValuevalue){
            resultList.clear();
            resultList.add(entry.getKey());
            currentMaxValuevalue = entry.getValue();
        } else if (entry.getValue() == currentMaxValuevalue){
            resultList.add(entry.getKey());
        }            
    }
    return resultList;
}

Comments

[CoolCK]

elegant solution, nicely explained.