Added Top K Frequent Elements

- Added Top K Frequent Elements and corresponding tests.

Author: hot9cups

Diff for: LeetcodeProblems/Algorithms/Top_K_Frequent_Elements.js

@@ -0,0 +1,54 @@
+/*
+Top K Frequent Elements
+https://leetcode.com/problems/top-k-frequent-elements/description/
+
+Given an integer array nums and an integer k, return the k most frequent elements. 
+You may return the answer in any order.
+
+
+Example 1:
+
+Input: nums = [1,1,1,2,2,3], k = 2
+Output: [1,2]
+
+
+Example 2:
+
+Input: nums = [1], k = 1
+Output: [1]
+ 
+
+Constraints:
+
+1) 1 <= nums.length <= 10^5
+2) -10^4 <= nums[i] <= 10^4
+3) k is in the range [1, the number of unique elements in the array].
+4) It is guaranteed that the answer is unique.
+*/
+
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number[]}
+ */
+ var topKFrequent = function(nums, k) {
+  const freqMap = new Map();
+  const bucket = [];
+  const result = [];
+  
+  for(let num of nums) {
+      freqMap.set(num, (freqMap.get(num) || 0) + 1);
+  }
+  
+  for(let [num, freq] of freqMap) {
+      bucket[freq] = (bucket[freq] || new Set()).add(num);
+  }
+  
+  for(let i = bucket.length-1; i >= 0; i--) {
+      if(bucket[i]) result.push(...bucket[i]);
+      if(result.length === k) break;
+  }
+  return result;
+};
+
+module.exports.topKFrequent = topKFrequent;

Diff for: LeetcodeProblemsTests/Algorithms/Top_K_Frequent_Elements_Test.js

@@ -0,0 +1,10 @@
+const assert = require('assert');
+const topKFrequent = require('../../LeetcodeProblems/Algorithms/Top_K_Frequent_Elements').topKFrequent;
+
+var test = function () {
+  assert.deepEqual(topKFrequent([1,1,1,2,2,3], 2).sort(), [1,2]);
+  assert.deepEqual(topKFrequent([7,8,9,8,9,8], 2).sort(), [8,9]);
+  assert.deepEqual(topKFrequent([1,1,1,1], 1).sort(), [1]);
+}
+
+module.exports.test = test;

Diff for: README.md

@@ -67,6 +67,7 @@ To run a specific problem in your console run  `node <problem_file_path>` (e.g.
 | [Find Subarrays With Equal Sum ](/LeetcodeProblems/Algorithms/Find_Subarrays_With_Equal_Sums.js)                | Medium | https://leetcode.com/problems/find-subarrays-with-equal-sum/ | 
 | [Reverse Integer](/LeetcodeProblems/Algorithms/Reverse_Integer.js)                                              | Medium | https://leetcode.com/problems/reverse-integer/ |
 | [Minimize Maximum Pair Sum in Array ](/LeetcodeProblems/Algorithms/Minimize_Maximum_Pair_Sum_In_Array.js)                                                   | Medium | https://leetcode.com/problems/minimize-maximum-pair-sum-in-array/ |
+| [Top K Frequent Elements ](/LeetcodeProblems/Algorithms/Top_K_Frequent_Elements.js)                                                   | Medium | https://leetcode.com/problems/top-k-frequent-elements/ |
 | [Flood Fill ](/LeetcodeProblems/Algorithms/Flood_Fill.js)                                                       | Easy   | https://leetcode.com/problems/flood-fill/ |
 | [Implement stack using queues ](/LeetcodeProblems/Algorithms/Implement_stack_using_queues.js)                   | Easy   | https://leetcode.com/problems/implement-stack-using-queues/ |
 | [Number of Segments in a String ](/LeetcodeProblems/Algorithms/Number_of_Segments_in_a_String.js)               | Easy   | https://leetcode.com/problems/number-of-segments-in-a-string/ |