get-distance-from-target.ts

// https://stackoverflow.com/a/19277804
function getFurthestFrom(target: number, list: number[]) {
	const outcome: string[] = [];
	let record = 0;

	for (const index in list) {
		const entry = list[index];
		const distance = Math.abs(entry - target);

		if (distance === record) {
			outcome.push(index);
		} else if (distance > record) {
			outcome.splice(0, outcome.length, index);
			record = distance;
		}
	}

	return outcome.map((entry) => [entry, list[entry]]);
}

function getClosestTo(target: number, list: number[]) {
	const outcome: string[] = [];
	let record = Infinity;

	for (const index in list) {
		const entry = list[index];
		const distance = Math.abs(entry - target);

		if (distance === record) {
			outcome.push(index);
		} else if (distance < record) {
			outcome.splice(0, outcome.length, index);
			record = distance;
		}
	}

	return outcome.map((entry) => [entry, list[entry]]);
}

function buildDistancePredicate(
	callback: (target: number, entry: number) => boolean,
	initial: number
) {
	return function (target: number, list: number[]) {
		const outcome: string[] = [];
		let record = initial;

		for (const index in list) {
			const entry = list[index];
			const distance = callback(target, entry);

			if (distance === record) {
				outcome.push(index);
			} else if (distance > record) {
				outcome.splice(0, outcome.length, index);
				record = distance;
			}
		}

		return outcome.map((entry) => [entry, list[entry]]);
	}
}

// Using the predicate in an attempt to reduce the code footprint
// Although the use of standardized code would likely be better to trace the stack

// const getFurthestFrom2 = buildDistancePredicate((target, entry) => Math.abs((entry - (target / 2)), 0);
// const getClosestTo2 = buildDistancePredicate((target, entry) => Math.abs((entry - (target / 2)), Infinity);
const getFurthestFromFactor = buildDistancePredicate((target, entry) => Math.abs((entry - (target / 2)) % target), 0);
const getClosestToFactor = buildDistancePredicate((target, entry) => Math.abs((entry - (target / 2)) % target), Infinity);

// console.log(getFurthestFrom(10, [5, 15]));
// console.log(getClosestTo(10, [5, 15]));

console.log(getFurthestFromFactor(20, [4, 5, 6, 15]));