# Heap sort

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]`

### Written by Angelos Chalaris

I'm Angelos Chalaris, a JavaScript software engineer, based in Athens, Greece. The best snippets from my coding adventures are published here to help others learn to code.

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