feat: add Top K Frequent Elements

Author: dukeluo

README.md

@@ -4,9 +4,10 @@ https://neetcode.io/roadmap
 
 ### Leetcode
 
-| #   | Title                                                                   | Difficulty | Solution                                             |
-| --- | ----------------------------------------------------------------------- | ---------- | ---------------------------------------------------- |
-| 217 | [Contains Duplicate](https://leetcode.com/problems/contains-duplicate/) | Easy       | [TypeScript](./TypeScript/217.contains-duplicate.ts) |
-| 242 | [Valid Anagram](https://leetcode.com/problems/valid-anagram/)           | Easy       | [TypeScript](./TypeScript/242.valid-anagram.ts)      |
-| 242 | [Two Sum](https://leetcode.com/problems/two-sum/)                       | Easy       | [TypeScript](./TypeScript/1.two-sum.ts)              |
-| 49  | [Group Anagrams](https://leetcode.com/problems/two-sum/)                | Medium     | [TypeScript](./TypeScript/49.group-anagrams.ts)      |
+| #   | Title                                                                             | Difficulty | Solution                                                  |
+| --- | --------------------------------------------------------------------------------- | ---------- | --------------------------------------------------------- |
+| 217 | [Contains Duplicate](https://leetcode.com/problems/contains-duplicate/)           | Easy       | [TypeScript](./TypeScript/217.contains-duplicate.ts)      |
+| 242 | [Valid Anagram](https://leetcode.com/problems/valid-anagram/)                     | Easy       | [TypeScript](./TypeScript/242.valid-anagram.ts)           |
+| 242 | [Two Sum](https://leetcode.com/problems/two-sum/)                                 | Easy       | [TypeScript](./TypeScript/1.two-sum.ts)                   |
+| 49  | [Group Anagrams](https://leetcode.com/problems/two-sum/)                          | Medium     | [TypeScript](./TypeScript/49.group-anagrams.ts)           |
+| 347 | [Top K Frequent Elements](https://leetcode.com/problems/top-k-frequent-elements/) | Medium     | [TypeScript](./TypeScript/347.top-k-frequent-elements.ts) |

TypeScript/347.top-k-frequent-elements.ts

@@ -0,0 +1,33 @@
+function topKFrequent(nums: number[], k: number): number[] {
+  const map = new Map<number, number>();
+
+  nums.forEach((n) => {
+    const frequency = map.get(n) ?? 0;
+
+    map.set(n, frequency + 1);
+  });
+
+  return Array.from(map)
+    .sort(([n1, f1], [n2, f2]) => f2 - f1)
+    .slice(0, k)
+    .map(([n, f]) => n);
+}
+
+function topKFrequent2(nums: number[], k: number): number[] {
+  const map = new Map<number, number>();
+  const count: number[][] = new Array(nums.length + 1).fill(0).map(() => []);
+  const result: number[] = [];
+
+  nums.forEach((n) => map.set(n, (map.get(n) ?? 0) + 1));
+  map.forEach((f, n) => count[f].push(n));
+
+  for (let i = count.length - 1; i >= 1; i--) {
+    for (let j = 0; j < count[i].length; j++) {
+      result.push(count[i][j]);
+
+      if (result.length === k) return result;
+    }
+  }
+
+  return result;
+}