One-Hundred-Sixty-Eight Commit: Add Maximum Distinct Elements problem to Top K Elements section

Author: AAdewunmi

src/Top_K_Elements/Problem_9_Maximum_Distinct_Elements.java

@@ -0,0 +1,50 @@
+package Top_K_Elements;
+
+// Problem Statement: Maximum Distinct Elements (medium)
+// LeetCode Question:
+
+import java.util.HashMap;
+import java.util.Map;
+import java.util.PriorityQueue;
+
+public class Problem_9_Maximum_Distinct_Elements {
+
+    public int findMaximumDistinctElements(int[] nums, int k) {
+        int distinctElementsCount = 0;
+        if (nums.length <= k)
+            return distinctElementsCount;
+
+        // find the frequency of each number
+        Map<Integer, Integer> numFrequencyMap = new HashMap<>();
+        for (int i : nums)
+            numFrequencyMap.put(i, numFrequencyMap.getOrDefault(i, 0) + 1);
+
+        PriorityQueue<Map.Entry<Integer, Integer>> minHeap =
+                new PriorityQueue<Map.Entry<Integer, Integer>>(
+                        (e1, e2) -> e1.getValue() - e2.getValue());
+
+        // insert all numbers with frequency greater than '1' into the min-heap
+        for (Map.Entry<Integer, Integer> entry : numFrequencyMap.entrySet()) {
+            if (entry.getValue() == 1)
+                distinctElementsCount++;
+            else
+                minHeap.add(entry);
+        }
+
+        // following a greedy approach, try removing the least frequent numbers first from
+        // the min-heap
+        while (k > 0 && !minHeap.isEmpty()) {
+            Map.Entry<Integer, Integer> entry = minHeap.poll();
+            // to make an element distinct, we need to remove all of its occurrences except one
+            k -= entry.getValue() - 1;
+            if (k >= 0)
+                distinctElementsCount++;
+        }
+
+        // if k > 0, this means we have to remove some distinct numbers
+        if (k > 0)
+            distinctElementsCount -= k;
+
+        return distinctElementsCount;
+    }
+}