Add quicksort

snippets/quickSort.md

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+---
+title: quickSort
+tags: algorithm,array,recursion,advanced
+---
+
+Sorts an array of numbers, using the quicksort algorithm.
+
+- Use recursion.
+- Use the spread operator (`...`) to clone the original array, `arr`.
+- If the `length` of the array is less than `2`, return the cloned array.
+- Use `Math.floor()` to calculate the index of the pivot element.
+- Use `Array.prototype.reduce()` and `Array.prototype.push()` to split the array into two subarrays (elements smaller or equal to the `pivot` and elements greater than it), destructuring the result into two arrays.
+- Recursively call `quickSort()` on the created subarrays.
+
+```js
+const quickSort = arr => {
+  const a = [...arr];
+
+  if (a.length < 2) return a;
+
+  const pivotIndex = Math.floor(arr.length / 2);
+  const pivot = a[pivotIndex];
+  const [lo, hi] = a.reduce(
+    (acc, val, i) => {
+      if (val < pivot || (val === pivot && i != pivotIndex)) {
+        acc[0].push(val);
+      } else if (val > pivot) {
+        acc[1].push(val);
+      }
+      return acc;
+    },
+    [[], []]
+  );
+
+  return [...quickSort(lo), pivot, ...quickSort(hi)];
+};
+```
+
+```js
+quickSort([1, 6, 1, 5, 3, 2, 1, 4]); // [1, 1, 1, 2, 3, 4, 5, 6]
+```