solves #2341: Maximum Number of Pairs in Array in java

Author: anishLearnsToCode

Diff for: README.md

@@ -751,7 +751,7 @@
 | 2331 | [Evaluate Boolean Binary Tree](https://leetcode.com/problems/evaluate-boolean-binary-tree)                                                                             |                                                                                  [![Java](assets/java.png)](src/EvaluateBooleanBinaryTree.java)                                                                                  |                                                                                                                                   |
 | 2335 | [Minimum Amount of Time to Fill Cups](https://leetcode.com/problems/minimum-amount-of-time-to-fill-cups)                                                               |                                                                                [![Java](assets/java.png)](src/MinimumAmountOfTimeToFillCups.java)                                                                                |                                                                                                                                   |
 | 2439 | [Minimize Maximum of Array](https://leetcode.com/problems/minimize-maximum-of-array)                                                                                   |                                                                               [![Python](assets/python.png)](python/minimize_maximum_of_array.py)                                                                                |                                                                                                                                   |
-| 2341 | [Maximum Number of Pairs in Array](https://leetcode.com/problems/maximum-number-of-pairs-in-array)                                                                     |                                                                                                                                                                                                                                  |                                                                                                                                   |
+| 2341 | [Maximum Number of Pairs in Array](https://leetcode.com/problems/maximum-number-of-pairs-in-array)                                                                     |                                                                                 [![Java](assets/java.png)](src/MaximumNumberOfPairsInArray.java)                                                                                 |                                                                                                                                   |
 | 2347 | [Best Poker Hand](https://leetcode.com/problems/best-poker-hand)                                                                                                       |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 2348 | [Number of Zero-Filled Subarrays](https://leetcode.com/problems/number-of-zero-filled-subarrays)                                                                       |                                                                            [![Python](assets/python.png)](python/number_of_zero_filled_subarrays.py)                                                                             |                                                                                                                                   |
 | 2351 | [First Letter to Appear Twice](https://leetcode.com/problems/first-letter-to-appear-twice)                                                                             |                                                                                                                                                                                                                                  |                                                                                                                                   |

Diff for: src/MaximumNumberOfPairsInArray.java

@@ -0,0 +1,30 @@
+// https://leetcode.com/problems/maximum-number-of-pairs-in-array
+// T: O(N)
+// S: O(N)
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class MaximumNumberOfPairsInArray {
+    public int[] numberOfPairs(int[] nums) {
+        final Map<Integer, Integer> digitFrequencies = getFrequencies(nums);
+        final int numberOfPairs = getNumberOfPairs(digitFrequencies);
+        return new int[] { numberOfPairs, nums.length - 2 * numberOfPairs };
+    }
+
+    private int getNumberOfPairs(Map<Integer, Integer> frequencies) {
+        int result = 0;
+        for (int frequency : frequencies.values()) {
+            result += frequency / 2;
+        }
+        return result;
+    }
+
+    private Map<Integer, Integer> getFrequencies(int[] array) {
+        final Map<Integer, Integer> result = new HashMap<>();
+        for (int element : array) {
+            result.put(element, result.getOrDefault(element, 0) + 1);
+        }
+        return result;
+    }
+}