@Test
	public void P17_havingEnoughMoney() {
		// when

		Map<String, Integer> items = shopList.stream()
				.map(Shop::getItemList)
				.flatMap(List::stream)
				.distinct()
				.collect(Collectors.toMap(i -> i.getName(), i -> i.getPrice(), (a, b) -> Math.min(a, b)));


		final List<String> customerNameList = customerList.stream()
				.filter(i -> sum(i.getWantToBuy(), items) <= i.getBudget())
				.filter(i -> haveall(i.getWantToBuy(), items))
				.map(Customer::getName)
				.collect(Collectors.toList());

		// then
		assertThat(customerNameList).hasSize(8);
		assertThat(customerNameList).containsOnly("Joe", "Steven", "Patrick", "Diana", "Kathy", "Alice", "Martin",
				"Amy");
	}

	private Long sum(List<ItemEntry> itemList, Map<String, Integer> priceLookup) {
		return itemList.stream()
				.collect(Collectors.summingLong(i -> priceLookup.getOrDefault(i.getName(), 0)));
	}

	private Boolean haveall(List<ItemEntry> itemList, Map<String, Integer> priceLookup) {
		return itemList.stream()
				.allMatch(i -> priceLookup.containsKey(i.getName()));
	}