Add optimized solution with O(n)

The changes include a new solution that does the job in O(n) as described in the video without sorting the frequency array taking O(logN)

Author: tayyabferozi

Diff for: javascript/0347-top-k-frequent-elements.js

@@ -1,5 +1,5 @@
 /**
- * Set - Frequency Counter
+ * Set - Frequency Counter | Using sort
  * Time O(NlogN) | Space O(N)
  * https://leetcode.com/problems/top-k-frequent-elements/
  * @param {number[]} nums
@@ -22,3 +22,44 @@ var topKFrequent = function(nums, k) {
     }
     return output;
 };
+
+/**
+ * Without Sort
+ * Time O(N) | Space O(k)
+ * https://leetcode.com/problems/top-k-frequent-elements/
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number[]}
+ */
+
+var topKFrequent = function(nums, k) {
+    const mp = new Map();
+    const arr = new Array(nums.length + 1).fill(0);
+    const ans = [];
+
+    nums.forEach(el => {
+        const val = mp.get(el) || 0;
+        mp.set(el, val + 1);
+    });
+
+    for ( let [key, value] of mp ) {
+        const prev = arr[value] || [];
+        prev.push(key);
+        arr[value] = prev;
+    }
+
+
+    arr.reverse();
+    for (let el of arr) {
+        if (k < 1) break;
+        if (el) {
+            for (let el2 of el) {
+                if (k < 1) break;
+                ans.push(el2);
+                k--;
+            }
+        }
+    }
+
+    return ans;
+};