public static void countSort(List<List<String>> arr) {
        int middle = arr.size() / 2;
        int temp[] = new int[100];
        
        Map<Integer, List<String>> map = new HashMap<>();
        
        // Traverse the list and populate hashmap
        // with keys being the "weight" of the pair.
        // Also replace the str to "-" if it is between [0..n/2].
        for(int i = 0; i < arr.size(); i++) {
            
            List<String> a = arr.get(i);
            int weight = Integer.parseInt(a.get(0));
            String str = a.get(1);
            
            if(i < middle) {
                str = "-";
            }
            
            temp[weight]++;
            
            if(map.containsKey(weight)) {
                map.get(weight).add(str);
            } else {
                map.put(weight, new ArrayList<String>());
                map.get(weight).add(str);
            }
        }
        
        // The base of count sort adapted to 
        // this challenge.
        for(int i = 0; i < temp.length; i++) {
            
            int repeat = temp[i];
            
            for (int j = 0; j < repeat; j++) {
                System.out.print(map.get(i).get(j) + " ");
            }
        }
        
    }