check2d
Version:
Polygons, Ellipses, Circles, Boxes, Lines, Points. Ray-Casting, offsets, rotation, scaling, padding, groups.
75 lines (74 loc) • 2.25 kB
JavaScript
;
Object.defineProperty(exports, "__esModule", { value: true });
exports.default = quickselect;
/**
* Rearranges items so that all items in the [left, k] are the smallest.
* The k-th element will have the (k - left + 1)-th smallest value in [left, right].
*
* @template T
* @param {T[]} arr the array to partially sort (in place)
* @param {number} k middle index for partial sorting (as defined above)
* @param {number} [left=0] left index of the range to sort
* @param {number} [right=arr.length-1] right index
* @param {(a: T, b: T) => number} [compare = (a, b) => a - b] compare function
*/
function quickselect(arr, k, left = 0, right = arr.length - 1, compare = defaultCompare) {
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(arr, k, newLeft, newRight, compare);
}
const t = arr[k];
let i = left;
/** @type {number} */
let j = right;
swap(arr, left, k);
if (compare(arr[right], t) > 0)
swap(arr, left, right);
while (i < j) {
swap(arr, i, j);
i++;
j--;
while (compare(arr[i], t) < 0)
i++;
while (compare(arr[j], t) > 0)
j--;
}
if (compare(arr[left], t) === 0)
swap(arr, left, j);
else {
j++;
swap(arr, j, right);
}
if (j <= k)
left = j + 1;
if (k <= j)
right = j - 1;
}
}
/**
* @template T
* @param {T[]} arr
* @param {number} i
* @param {number} j
*/
function swap(arr, i, j) {
const tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
/**
* @template T
* @param {T} a
* @param {T} b
* @returns {number}
*/
function defaultCompare(a, b) {
return a < b ? -1 : a > b ? 1 : 0;
}