add day 22

22-SortCharactersByFrequency.java

@@ -0,0 +1,33 @@
+class Solution {
+    public String frequencySort(String s) {
+        int len = s.length();
+        if (len == 0) return "";
+        int[] map = new int[128];
+        for (char c : s.toCharArray()) {
+            map[c - '\u0000']++;
+        }
+        // System.out.println(Arrays.toString(map));
+        PriorityQueue<Pair<Character, Integer>> pq = new PriorityQueue<>(new SortByFreq());
+        for (int i = 0; i < 128; i++) {
+            if (map[i] != 0) {
+                pq.add(new Pair((char) i, map[i]));
+            }
+        }
+
+        StringBuilder ans = new StringBuilder();
+        while (!pq.isEmpty()) {
+            Pair<Character, Integer> p = pq.poll();
+            for (int i = 0; i < p.getValue(); i++) {
+                ans.append(p.getKey());
+            }
+        }
+        return ans.toString();
+    }
+
+    class SortByFreq implements Comparator<Pair<Character, Integer>> {
+
+        public int compare(Pair<Character, Integer> p1, Pair<Character, Integer> p2) {
+            return p2.getValue() - p1.getValue();
+        }
+    }
+}