42 lines
1.1 KiB
TypeScript
42 lines
1.1 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] as T)) {
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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] as T);
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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 as T, ...perm]);
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}
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}
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return result;
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}
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