One-Hundred-Sixty-Seven Commit: Add 'K' Closest Numbers problem to Top K Elements section

Author: AAdewunmi

src/Top_K_Elements/Problem_5_K_Frequent_Numbers.java renamed to src/Top_K_Elements/Problem_5_Top_K_Frequent_Numbers.java

@@ -5,7 +5,7 @@
 
 import java.util.*;
 
-public class Problem_5_K_Frequent_Numbers {
+public class Problem_5_Top_K_Frequent_Numbers {
     public List<Integer> findTopKFrequentNumbers(int[] nums, int k) {
 
         Map<Integer, Integer> numFrequencyMap = new HashMap<>();

src/Top_K_Elements/Problem_8_K_Closest_Number.java

@@ -0,0 +1,64 @@
+package Top_K_Elements;
+
+// Problem Statement: 'K' Closest Numbers (medium)
+// LeetCode Question: 658. Find K Closest Elements
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.PriorityQueue;
+
+public class Problem_8_K_Closest_Number {
+
+    class Entry {
+        int key;
+        int value;
+
+        public Entry(int key, int value) {
+            this.key = key;
+            this.value = value;
+        }
+    }
+
+    public List<Integer> findClosestElements(int[] arr, int K, Integer X) {
+        int index = binarySearch(arr, X);
+        int low = index - K, high = index + K;
+        low = Math.max(low, 0); // 'low' should not be less than zero
+        // 'high' should not be greater the size of the array
+        high = Math.min(high, arr.length - 1);
+
+        PriorityQueue<Entry> minHeap = new PriorityQueue<>((n1, n2) -> n1.key - n2.key);
+        // add all candidate elements to the min heap, sorted by their absolute difference
+        // from 'X'
+        for (int i = low; i <= high; i++)
+            minHeap.add(new Entry(Math.abs(arr[i] - X), i));
+
+        // we need the top 'K' elements having smallest difference from 'X'
+        List<Integer> result = new ArrayList<>();
+        for (int i = 0; i < K; i++)
+            result.add(arr[minHeap.poll().value]);
+
+        Collections.sort(result);
+        return result;
+    }
+
+    private static int binarySearch(int[] arr, int target) {
+        int low = 0;
+        int high = arr.length - 1;
+        while (low <= high) {
+            int mid = low + (high - low) / 2;
+            if (arr[mid] == target)
+                return mid;
+            if (arr[mid] < target) {
+                low = mid + 1;
+            } else {
+                high = mid - 1;
+            }
+        }
+        if (low > 0) {
+            return low - 1;
+        }
+        return low;
+    }
+
+}