Add findFirstN, findLastN

snippets/findFirstN.md

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+---
+title: findFirstN
+tags: array,intermediate
+---
+
+Finds the first `n` elements for which the provided function returns a truthy value.
+
+- Use a `for..in` loop to execute the provided `matcher` for each element of `arr`.
+- Use `Array.prototype.push()` to append elements to the results array and return them if its `length` is equal to `n`.
+
+```js
+const findFirstN = (arr, matcher, n = 1) => {
+  let res = [];
+  for (let i in arr) {
+    const el = arr[i];
+    const match = matcher(el, i, arr);
+    if (match) res.push(el);
+    if (res.length === n) return res;
+  }
+  return res;
+};
+```
+
+```js
+findFirstN([1, 2, 4, 6], n => n % 2 === 0, 2); // [2, 4]
+findFirstN([1, 2, 4, 6], n => n % 2 === 0, 5); // [2, 4, 6]
+```

snippets/findLastN.md

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+---
+title: findLastN
+tags: array,intermediate
+---
+
+Finds the last `n` elements for which the provided function returns a truthy value.
+
+- Use a `for` loop to execute the provided `matcher` for each element of `arr`.
+- Use `Array.prototype.unshift()` to prepend elements to the results array and return them if its `length` is equal to `n`.
+
+```js
+const findLastN = (arr, matcher, n = 1) => {
+  let res = [];
+  for (let i = arr.length - 1; i >= 0; i--) {
+    const el = arr[i];
+    const match = matcher(el, i, arr);
+    if (match) res.unshift(el);
+    if (res.length === n) return res;
+  }
+  return res;
+};
+```
+
+```js
+findLastN([1, 2, 4, 6], n => n % 2 === 0, 2); // [4, 6]
+findLastN([1, 2, 4, 6], n => n % 2 === 0, 5); // [2, 4, 6]
+```