Add the Top K-Frequent Elements problem under the Sorting section

Author: subhatav

src/sorting/QuickKthSelect.java

@@ -6,7 +6,7 @@
 // Solution Link: https://leetcode.com/problems/kth-largest-element-in-an-array/solutions/60300/java-quick-select/
 
 // Approach: Use Quick Sorting with the Binary Search Technique
-// Average Time Complexity: O(N); Worst Time Complexity: O(N^2)
+// Average Time Complexity: O(N), Worst Time Complexity: O(N^2)
 
 public class QuickKthSelect {
 

src/sorting/QuickSortArray.java

@@ -5,7 +5,7 @@
 // Problem Link: https://leetcode.com/problems/sort-an-array/
 // Solution Link: https://leetcode.com/problems/sort-an-array/solutions/492042/7-sorting-algorithms-quick-sort-top-down-bottom-up-merge-sort-heap-sort-etc/
 
-// Average Time Complexity: O(NlogN); Worst Time Complexity: O(N^2); Worst Space Complexity: O(logN)
+// Average Time Complexity: O(NlogN), Worst Time Complexity: O(N^2); Worst Space Complexity: O(logN)
 
 public class QuickSortArray {
 

src/sorting/TopKFrequents.java

@@ -0,0 +1,59 @@
+package sorting;
+
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+
+// Problem Link: https://leetcode.com/problems/top-k-frequent-elements/
+// Solution Link: https://www.youtube.com/watch?v=YPTqKIgVk-k
+
+// Approach: Bucket Sort Technique; Time Complexity: O(N), Space Complexity: O(N)
+
+public class TopKFrequents {
+
+    public int[] compute(int[] nums, int k) {
+
+        @SuppressWarnings("unchecked")
+        List<Integer>[] buckets = new LinkedList[nums.length + 1];
+        Map<Integer, Integer> freqs = new HashMap<>();
+
+        int[] tops = new int[k];
+
+        for (int num : nums) {
+
+            int freq = freqs.getOrDefault(num, 0);
+
+            freqs.put(num, freq + 1);
+        }
+
+        for (int num : freqs.keySet()) {
+
+            int freq = freqs.get(num);
+
+            if (buckets[freq] == null) {
+
+                buckets[freq] = new LinkedList<>();
+            }
+
+            buckets[freq].add(num);
+        }
+
+        int index = k, freq = buckets.length;
+
+        while (--freq > 0 && k > 0) {
+
+            if (buckets[freq] != null) {
+
+                for (int num : buckets[freq]) {
+
+                    tops[index - k] = num;
+
+                    if (--k == 0) break;
+                }
+            }
+        }
+
+        return tops;
+    }
+}

src/sorting/UnsortedSubArray.java

@@ -8,7 +8,7 @@
 //              find their proper Indices in the Sorted whole-array; Time Complexity: O(N)
 
 public class UnsortedSubArray {
-    
+
     public int compute(int[] nums) {
 
         int last = nums.length - 1;
@@ -37,7 +37,7 @@ public int compute(int[] nums) {
             // = the unsorted sub-array AT LEAST needs to begin here
             if (nums[last - index] > low) left = last - index;
         }
-        
+
         return right - left + 1;
     }
 }