52 lines
1.4 KiB
TypeScript
52 lines
1.4 KiB
TypeScript
const bitIsSet = (num: number, pos: number) => (num & (1 << pos)) !== 0;
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export function encode<T>(all: readonly T[], set: Set<T>): number {
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let flags = 0;
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for (let i = 0; i < all.length; i++) {
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if (set.has(all[i])) {
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flags |= 1 << i;
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}
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}
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return flags;
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}
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export function decode<T>(all: readonly T[], flags: number): Set<T> {
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const total = 2 ** all.length;
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if (flags < 0 || flags >= total) throw Error("invalid flags");
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const decoded = new Set<T>();
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for (let j = 0; j < all.length; j++) {
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if (bitIsSet(flags, j)) decoded.add(all[j]);
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}
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return decoded;
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}
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export function* power<T>(xs: readonly T[]) {
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const total = 2 ** xs.length;
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for (let i = 0; i < total; i++) {
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yield decode(xs, i);
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}
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}
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export function permutations<T>(arr: readonly T[]): T[][] {
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if (arr.length === 0) return [[]];
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const result: T[][] = [];
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for (let i = 0; i < arr.length; i++) {
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const current = arr[i];
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const remaining = [...arr.slice(0, i), ...arr.slice(i + 1)];
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for (const perm of permutations(remaining)) {
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result.push([current, ...perm]);
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}
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}
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return result;
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}
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export function sample<T>(arr: readonly T[], n: number = arr.length): T[] {
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if (n > arr.length) return sample(arr, arr.length);
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const copy = [...arr];
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for (let i = 0; i < n; i++) {
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const j = i + Math.floor(Math.random() * (copy.length - i));
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[copy[i], copy[j]] = [copy[j] as T, copy[i] as T];
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}
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return copy.slice(0, n);
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}
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