Add write-up for LeetCode problem 2634. Filter Elements from Array (#409)

Author: miorel

workspaces/javascript-leetcode-month/problems/2634-filter-elements-from-array/README.md

@@ -2,7 +2,7 @@
 
 [View Problem on LeetCode](https://leetcode.com/problems/filter-elements-from-array/)
 
-This is one of many problems that essentially ask us to implement some built-in JavaScript function. Here, we're asked to implement filtering without using [`.filter`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter), so of course the first thing we should do is get accepted using `.filter`!
+This is one of several problems that essentially ask us to implement some built-in JavaScript function. Here, we're asked to implement filtering without using [`.filter`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/filter), so of course the first thing we should do is get accepted using `.filter`!
 
 For a more serious solution, a loop that builds the result works just fine.
 

workspaces/javascript-leetcode-month/problems/2634-filter-elements-from-array/solution.md

@@ -0,0 +1,13 @@
+function filter<T>(
+  arr: readonly T[],
+  fn: (element: T, index: number) => unknown,
+): T[] {
+  const res: T[] = [];
+
+  for (let i = 0; i < arr.length; ++i) {
+    const element = arr[i];
+    fn(element, i) && res.push(element);
+  }
+
+  return res;
+}

workspaces/javascript-leetcode-month/problems/2634-filter-elements-from-array/solutions/iterative-loops/using-classic-for.ts

@@ -0,0 +1,12 @@
+function filter<T>(
+  arr: readonly T[],
+  fn: (element: T, index: number) => unknown,
+): T[] {
+  const res: T[] = [];
+
+  arr.forEach((element, index) => {
+    fn(element, index) && res.push(element);
+  });
+
+  return res;
+}

workspaces/javascript-leetcode-month/problems/2634-filter-elements-from-array/solutions/iterative-loops/using-for-each.ts

@@ -0,0 +1,12 @@
+function filter<T>(
+  arr: readonly T[],
+  fn: (element: T, index: number) => unknown,
+): T[] {
+  const res: T[] = [];
+
+  for (const [index, element] of arr.entries()) {
+    fn(element, index) && res.push(element);
+  }
+
+  return res;
+}

workspaces/javascript-leetcode-month/problems/2634-filter-elements-from-array/solutions/iterative-loops/using-for-of-entries.ts

@@ -0,0 +1,13 @@
+function* lazyFilter<T>(
+  arr: readonly T[],
+  fn: (element: T, index: number) => unknown,
+): Generator<T, void, void> {
+  for (const [index, element] of arr.entries()) {
+    fn(element, index) && (yield element);
+  }
+}
+
+const filter = <T>(
+  arr: readonly T[],
+  fn: (element: T, index: number) => unknown,
+): T[] => Array.from(lazyFilter(arr, fn));

workspaces/javascript-leetcode-month/problems/2634-filter-elements-from-array/solutions/iterative-loops/using-generators.ts

@@ -0,0 +1,20 @@
+function filter<T>(
+  arr: readonly T[],
+  fn: (element: T, index: number) => unknown,
+): T[] {
+  const res: T[] = [];
+
+  const doFilter = (index: number) => {
+    if (index === arr.length) {
+      return;
+    }
+
+    const element = arr[index];
+    fn(element, index) && res.push(element);
+    doFilter(index + 1);
+  };
+
+  doFilter(0);
+
+  return res;
+}

workspaces/javascript-leetcode-month/problems/2634-filter-elements-from-array/solutions/recursive/inner-function.ts

@@ -0,0 +1,14 @@
+function filter<T>(
+  arr: readonly T[],
+  fn: (element: T, index: number) => unknown,
+  index: number = 0,
+  res: T[] = [],
+): T[] {
+  if (index === arr.length) {
+    return res;
+  }
+
+  const element = arr[index];
+  fn(element, index) && res.push(element);
+  return filter(arr, fn, index + 1, res);
+}

workspaces/javascript-leetcode-month/problems/2634-filter-elements-from-array/solutions/recursive/single-function-with-default-arguments.ts

@@ -0,0 +1,6 @@
+/**
+ * @param {number[]} arr
+ * @param {Function} fn
+ * @return {number[]}
+ */
+const filter = Function.prototype.call.bind(Array.prototype.filter);

workspaces/javascript-leetcode-month/problems/2634-filter-elements-from-array/solutions/using-built-in-filter/binding.js

@@ -0,0 +1,4 @@
+const filter = <T>(
+  arr: readonly T[],
+  fn: (element: T, index: number) => unknown,
+): T[] => arr.filter(fn);