# Heap sort

Angelos Chalaris · JavaScript, Algorithm, Array, Recursion · Dec 28, 2020

Sorts an array of numbers, using the heapsort algorithm.

• Use recursion.
• Use the spread operator (`...`) to clone the original array, `arr`.
• Use closures to declare a variable, `l`, and a function `heapify`.
• Use a `for` loop and `Math.floor()` in combination with `heapify` to create a max heap from the array.
• Use a `for` loop to repeatedly narrow down the considered range, using `heapify` and swapping values as necessary in order to sort the cloned array.
```const heapsort = arr => {
const a = [...arr];
let l = a.length;

const heapify = (a, i) => {
const left = 2 * i + 1;
const right = 2 * i + 2;
let max = i;
if (left < l && a[left] > a[max]) max = left;
if (right < l && a[right] > a[max]) max = right;
if (max !== i) {
[a[max], a[i]] = [a[i], a[max]];
heapify(a, max);
}
};

for (let i = Math.floor(l / 2); i >= 0; i -= 1) heapify(a, i);
for (i = a.length - 1; i > 0; i--) {
[a[0], a[i]] = [a[i], a[0]];
l--;
heapify(a, 0);
}
return a;
};```
`heapsort([6, 3, 4, 1]); // [1, 3, 4, 6]`

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