getNestedArraysMaxLength.js

function getNestedArraysMaxLength(inputArray) {
	let maxLength = -Infinity;
	const memory = [];

	inputArray.forEach(value => {
		memory[value] = findSeriesLength(inputArray, value, memory);
		maxLength = Math.max(maxLength, memory[value]);
	});

	return maxLength;
}

function findSeriesLength(arr, nextValue, memory) {
	const series = {[nextValue]: true};

	while (true) {
		nextValue = arr[nextValue];
		if (memory[nextValue]) {
			return memory[nextValue];
		}

		if (series[nextValue]) {
			return Object.keys(series).length;
		}
		series[nextValue] = true;
	}
}