451. Sort Characters By Frequencies

class Solution {
    public String frequencySort(String s) 
    {

      // Create a map to count the frequency of each character
        Map<Character, Integer> frequencyMap = new HashMap<>();
        for (char c : s.toCharArray())
         {
            frequencyMap.put(c, frequencyMap.getOrDefault(c, 0) + 1);
        }

        //Convert map to a list of characters sorted by frequency
        List<Character> characters = new ArrayList<>(frequencyMap.keySet());
        characters.sort((a, b) -> frequencyMap.get(b) - frequencyMap.get(a));

        // Build the result string based on the sorted characters
        StringBuilder result = new StringBuilder();
        for (char c : characters) 
        {
            int frequency = frequencyMap.get(c);
            for (int i = 0; i < frequency; i++)
             {
                result.append(c);
            }
        }

        return result.toString();
    }
}