solves sort array by incresing frequency

Author: anishLearnsToCode

README.md

@@ -405,7 +405,7 @@
 | 1619 | [Mean of Array After Removing Some Elements](https://leetcode.com/problems/mean-of-array-after-removing-some-elements)                                    |                                                      [![Java](assets/java.png)](src/MeanOfArrayAfterRemovingSomeElements.java)                                                       |                                                                                                                                   |
 | 1624 | [Largest Substring Between Two Equal Characters](https://leetcode.com/problems/largest-substring-between-two-equal-characters)                            |                                                    [![Java](assets/java.png)](src/LargestSubStringBetweenTwoEqualCharacters.java)                                                    |                                                                                                                                   |
 | 1629 | [Slowest Key](https://leetcode.com/problems/slowest-key)                                                                                                  |                                                                   [![Java](assets/java.png)](src/SlowestKey.java)                                                                    |                                                                                                                                   |
-| 1636 | [Sort Array by Increasing Frequency](https://leetcode.com/problems/sort-array-by-increasing-frequency)                                                    |                                                                                                                                                                                      |                                                                                                                                   |
+| 1636 | [Sort Array by Increasing Frequency](https://leetcode.com/problems/sort-array-by-increasing-frequency)                                                    |                                                         [![Java](assets/java.png)](src/SortArrayByIncreasingFrequency.java)                                                          |                                                                                                                                   |
 | 1640 | [Check Array Formation Through Concatenation](https://leetcode.com/problems/check-array-formation-through-concatenation)                                  |                                                                                                                                                                                      |                                                                                                                                   |
 | 1646 | [Get Maximum in Generated Array](https://leetcode.com/problems/get-maximum-in-generated-array)                                                            |                                                                                                                                                                                      |                                                                                                                                   |
 | 1652 | [Defuse the Bomb](https://leetcode.com/problems/defuse-the-bomb)                                                                                          |                                                                                                                                                                                      |                                                                                                                                   |

src/SortArrayByIncreasingFrequency.java

@@ -0,0 +1,32 @@
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+public class SortArrayByIncreasingFrequency {
+    public int[] frequencySort(int[] array) {
+        Map<Integer, Integer> frequencies = getFrequencies(array);
+
+        return toArray(Arrays.stream(array).boxed().sorted((a, b) -> {
+            if (frequencies.get(a).equals(frequencies.get(b))) return b - a;
+            return frequencies.get(a) - frequencies.get(b);
+        }).collect(Collectors.toList()));
+    }
+
+    private Map<Integer, Integer> getFrequencies(int[] array) {
+        final Map<Integer, Integer> frequencies = new HashMap<>();
+        for (int element : array) {
+            frequencies.put(element, frequencies.getOrDefault(element, 0) + 1);
+        }
+        return frequencies;
+    }
+
+    private int[] toArray(List<Integer> list) {
+        final int[] array = new int[list.size()];
+        for (int index = 0 ; index < list.size() ; index++) {
+            array[index] = list.get(index);
+        }
+        return array;
+    }
+}