# Quick sort

Isabelle Viktoria Maciohsek · JavaScript, Algorithm, Array, Recursion · Oct 13, 2021

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. The first one contains elements smaller than or equal to `pivot` and the second on elements greather than it. Destructure the result into two arrays.
• Recursively call `quickSort()` on the created subarrays.
```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)];
};```
`quickSort([1, 6, 1, 5, 3, 2, 1, 4]); // [1, 1, 1, 2, 3, 4, 5, 6]`

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