如何从Java列表中删除所有重复的字符串？

Question

对于给定的列表,假设[ "a", "a", "b", "c", "c" ]我需要[ "b" ](仅非重复元素)作为输出.请注意,这与使用Set作业界面不同...

我在Java中编写了以下代码来执行此操作:

void unique(List<String> list) {
    Collections.sort(list);
    List<String> dup = new ArrayList<>();
    int i = 0, j = 0;

    for (String e : list) {
        i = list.indexOf(e);
        j = list.lastIndexOf(e);

        if (i != j && !dup.contains(e)) {
            dup.add(e);
        }
    }

    list.removeAll(dup);
}

它有效...但是对于大小为85320的列表,几分钟后结束!

Answer 1

你最好的表现是设置:

    String[] xs = { "a", "a", "b", "c", "c" };

    Set<String> singles = new TreeSet<>();
    Set<String> multiples = new TreeSet<>();

    for (String x : xs) {
        if(!multiples.contains(x)){
            if(singles.contains(x)){
                singles.remove(x);
                multiples.add(x);
            }else{
                singles.add(x);
            }
        }
    }

它是单个传递,插入,删除和包含是log(n).

Answer 2

使用Java 8流:

return list.stream()
    .collect(Collectors.groupingBy(e -> e, Collectors.counting()))
    .entrySet()
    .stream()
    .filter(e -> e.getValue() == 1)
    .map(Map.Entry::getKey)
    .collect(Collectors.toList());