utils.ts

export function* choose<T>(items: T[], k: number, start = 0, output = new Array<T>(k)): IterableIterator<T[]> {
	if (!k) {
		yield output
		return
	}
	for (let chosen = start; chosen <= items.length - k; chosen++) {
		output[output.length - k] = items[chosen]
		yield* choose(items, k - 1, chosen + 1, output)
	}
}
export const rand = (n: number): number => (Math.random() * n) | 0 //random number from 0 to n - 1
export const times = <A>(f: () => A, n: number): A[] => new Array<A>(n).fill(0 as any).map(f) //n items generated by f
export function transpose<A>(m: A[][]): A[][] { //assumes m is square
	const {length} = m
	const mT = new Array<A[]>(length)
	for (let i = 0; i < length; i++) {
		const mTi = new Array<A>(length)
		for (let j = 0; j < length; j++) mTi[j] = m[j][i]
		mT[i] = mTi
	}
	return mT
}
export function* zip<A, B>(iter1: Iterable<A>, iter2: Iterable<B>): Iterable<[A, B]> {
	const iterator1 = iter1[Symbol.iterator](), iterator2 = iter2[Symbol.iterator]()
	let item1: IteratorResult<A>, item2: IteratorResult<B>
	while (!((item1 = iterator1.next()).done || (item2 = iterator2.next()).done)) yield [item1.value, item2.value]
}