实现使用Java计算一个字符串数组中每个字符串存在次数的算法的最快方法

Question

Just wondering what the quickest way to Implement an algorithm to count how many times each string is present in an array of strings using Java would be?

this is what i have tried and it works but im worried it might be "cheating" as it strays away from the question a bit:

{
    String[] stringArray = {"Random", "Words", "Here","Random", "Words", "Here","Random", "Words", "Here","Random", "Words", "Here"};

    List asList = Arrays.asList(stringArray);
    Set<String> mySet = new HashSet<>(asList);

    mySet.stream().forEach((s) -> {
        System.out.println(s + " " +Collections.frequency(asList,s));
    });
}

Answer 1

The easiest way is to use Map#merge() :

Map<String, Integer> m = new HashMap<>();
for (String s : array)
    m.merge(s, 1, Integer::sum);

after that, m will hold strings as keys and occurrences as values:

m.forEach((k, v) -> System.out.format("%s occured %s time(s)\n", k, v));

Answer 2

By using Collectors in streams:

Arrays.stream(list).collect(Collectors.groupingBy(e -> e, Collectors.counting()))

So, if you have something like this:

        String[] list = new String[4];
        list[0] = "something";
        list[1] = "gfddfgdfg";
        list[2] = "something";
        list[3] = "somet444hing";
        System.out.println(Arrays.stream(list).collect(Collectors.groupingBy(e -> e, Collectors.counting())));

output will be:

{gfddfgdfg=1, something=2, somet444hing=1}

Answer 3

I would use the groupingBy to return a map of counts.

Map<String, Long> counts = Stream.of(array)
                           .collect(Collectors.groupingBy(w -> w, Collectors.counting()));

to print these as well you can do

Stream.of(array)
      .collect(Collectors.groupingBy(w -> w, Collectors.counting()))
      .forEach((k, v) -> System.out.println(k + " occurred " + v " times));