solves #2475: Number of Unequal Triplets in Array in java

Author: anishLearnsToCode

README.md

@@ -781,7 +781,7 @@
 | 2465 | [Number of Distinct Averages](https://leetcode.com/problems/number-of-distinct-averages)                                                                               |                                                                                  [![Java](assets/java.png)](src/NumberOfDistinctAverages.java)                                                                                   |                                                                                                                                   |
 | 2466 | [Count Ways To Build Good Strings](https://leetcode.com/problems/count-ways-to-build-good-strings)                                                                     |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 2469 | [Convert the Temperature](https://leetcode.com/problems/convert-the-temperature)                                                                                       |                                                                                    [![Java](assets/java.png)](src/ConvertTheTemperature.java)                                                                                    |                                                                                                                                   |
-| 2475 | [Number of Unequal Triplets in Array](https://leetcode.com/problems/number-of-unequal-triplets-in-array)                                                               |                                                                                                                                                                                                                                  |                                                                                                                                   |
+| 2475 | [Number of Unequal Triplets in Array](https://leetcode.com/problems/number-of-unequal-triplets-in-array)                                                               |                                                                               [![Java](assets/java.png)](src/NumberOfUnequalTripletsInArray.java)                                                                                |                                                                                                                                   |
 | 2481 | [Minimum Cuts to Divide a Circle](https://leetcode.com/problems/minimum-cuts-to-divide-a-circle)                                                                       |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 2485 | [Find the Pivot Integer](https://leetcode.com/problems/find-the-pivot-integer)                                                                                         |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 2490 | [Circular Sentence](https://leetcode.com/problems/circular-sentence)                                                                                                   |                                                                                                                                                                                                                                  |                                                                                                                                   |

src/NumberOfUnequalTripletsInArray.java

@@ -0,0 +1,21 @@
+// https://leetcode.com/problems/number-of-unequal-triplets-in-array
+// T: O(N)
+// S: O(N)
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class NumberOfUnequalTripletsInArray {
+    public int unequalTriplets(int[] array) {
+        final Map<Integer, Integer> frequency = new HashMap<>();
+        int pairs = 0, triplets = 0;
+        for (int index = 0 ; index < array.length ; index++) {
+            frequency.put(array[index], frequency.getOrDefault(array[index], 0) + 1);
+            final int pairsWithElement =  index + 1 - frequency.getOrDefault(array[index], 0);
+            pairs += pairsWithElement;
+            final int pairsWithoutElement = pairs - pairsWithElement * frequency.getOrDefault(array[index], 0);
+            triplets += pairsWithoutElement;
+        }
+        return triplets;
+    }
+}