Nth highest salary using Java Streams API

Prerequisite: One should know how to open streams on Map and how to use sorted by passing Comparator.

Consider the following map as input

Map<String,Integer> map = new HashMap<>();
        map.put("anil",1000);
        map.put("ankit",1200);
        map.put("bhavna",1300);
        map.put("james",1400);
        map.put("micael",1500);
        map.put("tom",1600);
        map.put("daniel",1700);

We want to fetch second highest salary with employee name. This can be achieved by below code.

Map.Entry<String,Integer> finalResult = map.entrySet()
          .stream()
          .sorted(Comparator.comparing(entry -> -entry.getValue())) // minus make it to do in desc order
          .toList()
          .get(1); // index start from 0

It’s quite simple, we just sort the Map.Entry with value and fetch the second element. But then interviewer will come with the below data and above solution fails.

Map<String,Integer> map2 = new HashMap<>();
        map2.put("anil",1000);
        map2.put("ankit",1200);
        map2.put("bhavna",1200);
        map2.put("james",1200);
        map2.put("micael",1000);
        map2.put("tom",1300);
        map2.put("daniel",1300);

Now get(1) will return any random value with either tom or daniel. The trick to solve this issue is to invert the map like below

finalResult = [1000=[micael, anil], 1200=[ankit, james, bhavna], 1300=[daniel, tom]]

This can be achieved with below code.

Map<Integer,List<String>> interimResult = 
   map2.entrySet()
    .stream()
    .collect(Collectors.groupingBy(entry ->entry.getValue(),
          Collectors.mapping(entry -> entry.getKey(),Collectors.toList())
    ));

Now we have inverted the map and result will be like below but in random order.

 {1200=[ankit, james, bhavna], 1300=[daniel, tom], 1000=[micael, anil]}

Now we just need to sort the map based on keys now. This can be easily done with below line of code.

List<Map.Entry<Integer, List<String>>> finalResult2 = map2.entrySet()
      .stream()
      .collect(Collectors.groupingBy(entry ->entry.getValue(),
          Collectors.mapping(entry -> entry.getKey(),Collectors.toList())
          ))
      .entrySet()
      .stream()
      .sorted(Comparator.comparing(it -> -it.getKey())) // minus sign for decreasing order
      .toList();

Now we just need to put .get(n-1) to find the nth largest salary and their respective employee names.

So, final code will look like

 Map.Entry<Integer,List<String>> finalResult2 = map2.entrySet()
        .stream()
        .collect(Collectors.groupingBy(entry ->entry.getValue(),
                        Collectors.mapping(entry -> entry.getKey(),Collectors.toList())
                        ))
        .entrySet()
        .stream()
        .sorted(Comparator.comparing(it -> it.getKey()))
        .toList()
        .get(1);

with result as below

1200=[ankit, james, bhavna]

That’s all from my side.

Find my GitHub link for this code

GitHub - anilgola90/javainterviewquestions

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