quickselect.js
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quickselect.js
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	import ascending from "./ascending.js";

	// Based on https://github.com/mourner/quickselect
	// ISC license, Copyright 2018 Vladimir Agafonkin.
	export default function quickselect(array, k, left = 0, right = array.length - 1, compare = ascending) {
	while (right > left) {
	if (right - left > 600) {
	const n = right - left + 1;
	const m = k - left + 1;
	const z = Math.log(n);
	const s = 0.5 * Math.exp(2 * z / 3);
	const sd = 0.5 * Math.sqrt(z * s * (n - s) / n) * (m - n / 2 < 0 ? -1 : 1);
	const newLeft = Math.max(left, Math.floor(k - m * s / n + sd));
	const newRight = Math.min(right, Math.floor(k + (n - m) * s / n + sd));
	quickselect(array, k, newLeft, newRight, compare);
	}

	const t = array[k];
	let i = left;
	let j = right;

	swap(array, left, k);
	if (compare(array[right], t) > 0) swap(array, left, right);

	while (i < j) {
	swap(array, i, j), ++i, --j;
	while (compare(array[i], t) < 0) ++i;
	while (compare(array[j], t) > 0) --j;
	}

	if (compare(array[left], t) === 0) swap(array, left, j);
	else ++j, swap(array, j, right);

	if (j <= k) left = j + 1;
	if (k <= j) right = j - 1;
	}
	return array;
	}

	function swap(array, i, j) {
	const t = array[i];
	array[i] = array[j];
	array[j] = t;
	}