Move all solutions into separate directory (cleanup)

the beginning

solutions/sort-array-by-increasing-frequency/Solution.java

@@ -0,0 +1,27 @@
+// Accepted
+// Runtime: 4 ms
+// Memory Usage: 39.1 MB
+// Submitted: January 15th, 2021
+
+class Solution {
+    public int[] frequencySort(int[] nums) {
+        Map<Integer, Integer> count = new HashMap<Integer, Integer>();
+        for (int n : nums)
+            count.put(n, count.getOrDefault(n, 0) + 1);
+        
+        PriorityQueue<Map.Entry<Integer, Integer>> pq = new PriorityQueue<>((a, b) -> a.getValue() != b.getValue() ? a.getValue() - b.getValue() : b.getKey() - a.getKey());
+        pq.addAll(count.entrySet());
+        
+        int[] sorted = new int[nums.length];
+        int i = 0;
+        while(!pq.isEmpty()) {
+            Map.Entry<Integer, Integer> entry = pq.poll();
+            int k = entry.getKey();
+            int v = entry.getValue();
+            while (v-- > 0)
+                sorted[i++] = k;
+        }
+        
+        return sorted;
+    }
+}