solves #2670: Find the Distinct Difference Array in java

Author: anishLearnsToCode

README.md

@@ -820,5 +820,5 @@
 | 2652 | [Sum Multiples](https://leetcode.com/problems/sum-multiples)                                                                                                           |                                                                                        [![Java](assets/java.png)](src/SumMultiples.java)                                                                                         |                                                                                                                                   |
 | 2656 | [Maximum Sum With Exactly K Elements](https://leetcode.com/problems/maximum-sum-with-exactly-k-elements)                                                               |                                                                               [![Java](assets/java.png)](src/MaximumSumWithExactlyKElements.java)                                                                                |                                                                                                                                   |
 | 2660 | [Determine the Winner of a Bowling Game](https://leetcode.com/problems/determine-the-winner-of-a-bowling-game)                                                         |                                                                              [![Java](assets/java.png)](src/DetermineTheWinnerOfABowlingGame.java)                                                                               |                                                                                                                                   |
-| 2670 | [Find the Distinct Difference Array](https://leetcode.com/problems/find-the-distinct-difference-array)                                                                 |                                                                                                                                                                                                                                  |                                                                                                                                   |
+| 2670 | [Find the Distinct Difference Array](https://leetcode.com/problems/find-the-distinct-difference-array)                                                                 |                                                                               [![Java](assets/java.png)](src/FindTheDistinctDifferenceArray.java)                                                                                |                                                                                                                                   |
 | 2678 | [Number of Senior Citizens](https://leetcode.com/problems/number-of-senior-citizens)                                                                                   |                                                                                                                                                                                                                                  |                                                                                                                                   |

src/FindTheDistinctDifferenceArray.java

@@ -0,0 +1,42 @@
+// https://leetcode.com/problems/find-the-distinct-difference-array
+// N: length of array
+// T: O(N)
+// S: O(N)
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class FindTheDistinctDifferenceArray {
+    public int[] distinctDifferenceArray(int[] nums) {
+        final Map<Integer, Integer> leftFrequencies = new HashMap<>();
+        final Map<Integer, Integer> rightFrequencies = getNumberFrequencies(nums);
+        final int[] result = new int[nums.length];
+        int k = 0;
+        for (int element : nums) {
+            addToFrequency(leftFrequencies, element);
+            removeFromFrequency(rightFrequencies, element);
+            result[k++] = leftFrequencies.size() - rightFrequencies.size();
+        }
+        return result;
+    }
+
+    private void removeFromFrequency(Map<Integer, Integer> frequencies, int element) {
+        if (frequencies.get(element) == 1) {
+            frequencies.remove(element);
+        } else {
+            frequencies.put(element, frequencies.getOrDefault(element, 0) - 1);
+        }
+    }
+
+    private void addToFrequency(Map<Integer, Integer> frequencies, int element) {
+        frequencies.put(element, frequencies.getOrDefault(element, 0) + 1);
+    }
+
+    private Map<Integer, Integer> getNumberFrequencies(int[] array) {
+        final Map<Integer, Integer> result = new HashMap<>();
+        for (int element : array) {
+            result.put(element, result.getOrDefault(element, 0) + 1);
+        }
+        return result;
+    }
+}