프로그래머스: 위장

public int solution(String[][] clothes) {
    Map<String, Integer> map = new HashMap<String, Integer>();

    for (String[] s : clothes) {
        int value = 1;
        String key = s[1];
        if (map.containsKey(key)) {
            value = map.get(key);
        }

        map.put(key, ++value);
    }

    int answer = 1;
    for (Map.Entry<String, Integer> entry : map.entrySet()) {
        answer *= entry.getValue();
    }

    return answer - 1;
}

public int solution(String[][] clothes) {
    return Arrays.stream(clothes)
            .collect(groupingBy(p -> p[1], mapping(p -> p[0], counting())))
            .values()
            .stream()
            .collect(reducing(1L, (x, y) -> x * (y + 1))).intValue() - 1;
}

assertEquals(5, test.solution(new String[][] {{"yellow_hat", "headgear"}, {"blue_sunglasses", "eyewear"}, {"green_turban", "headgear"}}));
assertEquals(3, test.solution(new String[][] {{"crow_mask", "face"}, {"blue_sunglasses", "face"}, {"green_turban", "face"}}));