43 lines
1.3 KiB
Markdown
43 lines
1.3 KiB
Markdown
---
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title: Quick sort
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tags: algorithm,array,recursion
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author: maciv
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cover: blog_images/eagle.jpg
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firstSeen: 2017-12-28T13:42:41+02:00
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lastUpdated: 2021-10-13T19:29:39+02:00
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---
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Sorts an array of numbers, using the quicksort algorithm.
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- Use recursion.
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- Use the spread operator (`...`) to clone the original array, `arr`.
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- If the `length` of the array is less than `2`, return the cloned array.
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- Use `Math.floor()` to calculate the index of the pivot element.
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- 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 greater than it. Destructure the result into two arrays.
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- Recursively call `quickSort()` on the created subarrays.
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```js
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const quickSort = arr => {
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const a = [...arr];
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if (a.length < 2) return a;
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const pivotIndex = Math.floor(arr.length / 2);
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const pivot = a[pivotIndex];
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const [lo, hi] = a.reduce(
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(acc, val, i) => {
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if (val < pivot || (val === pivot && i != pivotIndex)) {
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acc[0].push(val);
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} else if (val > pivot) {
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acc[1].push(val);
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}
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return acc;
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},
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[[], []]
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);
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return [...quickSort(lo), pivot, ...quickSort(hi)];
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};
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```
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```js
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quickSort([1, 6, 1, 5, 3, 2, 1, 4]); // [1, 1, 1, 2, 3, 4, 5, 6]
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```
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