feat(solution): Added solutions for problem 2620, 2634, 2635

Author: maxchui

1001-9999.md

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+# Problems 1001-9999 <!-- omit from toc -->
+
+## Algorithms <!-- omit from toc -->
+
+- [JavaScript/TypeScript](#javascripttypescript)
+
+## JavaScript/TypeScript
+
+|  #  | Title           |  Solution       |  Time           | Space           | Difficulty    | Tag          | Note|  
+|-----|---------------- | --------------- | --------------- | --------------- | ------------- |--------------|-----|
+|2620|[Counter](https://leetcode.com/problems/counter/)| [TypeScript](./TypeScript/2620-Counter.ts)| $O(1)$| $O(1)$|Easy||`Closure` </br>`Higher Order Function` </br> `Function Factory`|
+|2634|[Filter Elements From Array](https://leetcode.com/problems/filter-elements-from-array/)| [TypeScript](./TypeScript/2634-Filter_Elements_From_Array.ts)| $O(n)$| $O(n)$|Easy|||
+|2635|[Apply Transform Over Each Element in Array](https://leetcode.com/problems/apply-transform-over-each-element-in-array/)| [TypeScript](./TypeScript/2635-Apply_Transform_Over_Each_Element_In_Array.ts)| $O(n)$| $O(n)$|Easy||`Higher Order Function` </br> `Callback Function`|

TypeScript/2620-Counter.ts

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+// URL: https://leetcode.com/problems/counter/
+// Time Complexity: O(1)
+// Space Complexity: O(1)
+
+// Solution: Create a closure function that returns a function that increments the counter by 1 each time it is called.
+function createCounter(n: number): () => number {
+  let counter: number = n;
+
+  return function () {
+    return counter++;
+  };
+}
+
+/**
+ * const counter = createCounter(10)
+ * counter() // 10
+ * counter() // 11
+ * counter() // 12
+ */

TypeScript/2634-Filter_Elements_From_Array.ts

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+// URL: https://leetcode.com/problems/filter-elements-from-array/
+// Time Complexity: O(n)
+// Space Complexity: O(n)
+
+type Fn = (n: number, i: number) => any;
+
+function filter(arr: number[], fn: Fn): number[] {
+  const tempArr: number[] = [];
+
+  arr.forEach((element, index) => {
+    if (fn(element, index)) {
+      tempArr.push(element);
+    }
+  });
+
+  return tempArr;
+}

TypeScript/2635-Apply_Transform_Over_Each_Element_In_Array.ts

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+// URL: https://leetcode.com/problems/apply-transform-over-each-element-in-array/
+// Time Complexity: O(n)
+// Space Complexity: O(n)
+
+function map(arr: number[], fn: (n: number, i: number) => number): number[] {
+  const transformedArr: number[] = [];
+
+  arr.forEach((num, index) => {
+    transformedArr[index] = fn(num, index);
+  });
+
+  return transformedArr;
+}