Add 451_Sort_Characters_By_Frequency.java

Author: Sean Prashad

Top K Elements/451_Sort_Characters_By_Frequency.java

@@ -0,0 +1,27 @@
+class Solution {
+ public String frequencySort(String s) {
+ if (s == null || s.length() == 0) {
+ return s;
+ }
+
+ HashMap<Character, Integer> hm = new HashMap<>();
+ PriorityQueue<Map.Entry<Character, Integer>> pq = new PriorityQueue<>((a, b) -> b.getValue() - a.getValue());
+ StringBuilder sb = new StringBuilder();
+
+ for (char c : s.toCharArray()) {
+ hm.put(c, hm.getOrDefault(c, 0) + 1);
+ }
+
+ pq.addAll(hm.entrySet());
+
+ while (!pq.isEmpty()) {
+ Map.Entry<Character, Integer> entry = pq.poll();
+
+ for (int i = 0; i < entry.getValue(); i++) {
+ sb.append(entry.getKey());
+ }
+ }
+
+ return sb.toString();
+ }
+}