solves #2190: Most Frequent Number Following Key In an Array in java

Author: anishLearnsToCode

Diff for: README.md

@@ -716,7 +716,7 @@
 | 2176 | [Count Equal and Divisible Pairs in an Array](https://leetcode.com/problems/count-equal-and-divisible-pairs-in-an-array)                                               |                                                                            [![Java](assets/java.png)](src/CountEqualAndDivisiblePairsInAnArray.java)                                                                             |                                                                                                                                   |
 | 2180 | [Count Integers With Even Digit Sum](https://leetcode.com/problems/count-integers-with-even-digit-sum)                                                                 |                                                                                [![Java](assets/java.png)](src/CountIntegersWithEvenDigitSum.java)                                                                                |                                                                                                                                   |
 | 2185 | [Counting Words With a Given Prefix](https://leetcode.com/problems/counting-words-with-a-given-prefix)                                                                 |                                                                                [![Java](assets/java.png)](src/CountingWordsWithAGivenPrefix.java)                                                                                |                                                                                                                                   |
-| 2190 | [Most Frequent Number Following Key In an Array](https://leetcode.com/problems/most-frequent-number-following-key-in-an-array)                                         |                                                                                                                                                                                                                                  |                                                                                                                                   |
+| 2190 | [Most Frequent Number Following Key In an Array](https://leetcode.com/problems/most-frequent-number-following-key-in-an-array)                                         |                                                                           [![Java](assets/java.png)](src/MostFrequentNumberFollowingKeyInAnArray.java)                                                                           |                                                                                                                                   |
 | 2194 | [Cells in a Range on an Excel Sheet](https://leetcode.com/problems/cells-in-a-range-on-an-excel-sheet)                                                                 |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 2200 | [Find All K-Distant Indices in an Array](https://leetcode.com/problems/find-all-k-distant-indices-in-an-array)                                                         |                                                                                                                                                                                                                                  |                                                                                                                                   |
 | 2206 | [Divide Array Into Equal Pairs](https://leetcode.com/problems/divide-array-into-equal-pairs)                                                                           |                                                                                                                                                                                                                                  |                                                                                                                                   |

Diff for: src/MostFrequentNumberFollowingKeyInAnArray.java

@@ -0,0 +1,35 @@
+// https://leetcode.com/problems/most-frequent-number-following-key-in-an-array
+// T: O(N)
+// S: O(N)
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class MostFrequentNumberFollowingKeyInAnArray {
+    public int mostFrequent(int[] nums, int key) {
+        final Map<Integer, Integer> targetToFrequency = getTargetFrequencies(nums, key);
+        return mostFrequentTarget(targetToFrequency);
+    }
+
+    private Map<Integer, Integer> getTargetFrequencies(int[] array, int key) {
+        final Map<Integer, Integer> result = new HashMap<>();
+        for (int index = 0 ; index < array.length - 1 ; index++) {
+            if (array[index] == key) {
+                int target = array[index + 1];
+                result.put(target, result.getOrDefault(target, 0) + 1);
+            }
+        }
+        return result;
+    }
+
+    private int mostFrequentTarget(final Map<Integer, Integer> frequencies) {
+        int target = -1, maxFrequency = -1;
+        for (Map.Entry<Integer, Integer> entry : frequencies.entrySet()) {
+            if (entry.getValue() > maxFrequency) {
+                maxFrequency = entry.getValue();
+                target = entry.getKey();
+            }
+        }
+        return target;
+    }
+}