检查重复列表Java 8

Question

给定n个列表,我想知道是否有任何两个列表具有完全相同的元素.下面是Java 7中的代码.

public static <T> boolean hasduplicateList(List<List<T>> lists) {
    for (List<T> outerList : lists) {
        int count = 0;
        Set<T> outerSet = new HashSet<>(outerList);
        for (List<T> innerList : lists) {
            Set<T> innerSet = new HashSet<>(innerList);
            if (outerSet.equals(innerSet)) {
                count++;
            }
            if (count == 2) {
                return true;
            }
        }
    }
    return false;
}

是否有更好的方法来实现特别使用Java8？

Answer 1

因为在Java 7代码中List,Set在比较之前将s 转换为s ,似乎您要检查输入中是否至少有2个List具有相同的元素集(忽略重复或顺序).

您可以通过流式传输List并将其转换Stream为Sets 来在Java 8中实现此目的.然后你要做的就是找出不同Sets 的数量是否小于输入的大小List:

public static <T> boolean hasduplicateList(List<List<T>> lists) {
  return 
    lists.stream()  // create a <Stream<List<T>>
         .map(HashSet::new) // transform Stream<List<T>> to Stream<HashSet<T>> 
         .distinct() // keep only distinct Sets
         .count() < lists.size();
}

测试:

public static void main (String[] args)
{ 
    List<String> alist = Arrays.asList ("a","b","c");
    List<String> blist = Arrays.asList ("b","c","c","a");
    List<String> clist = Arrays.asList ("e","d","c","a");
    List<List<String>> llist1 = Arrays.asList (alist,blist);
    List<List<String>> llist2 = Arrays.asList (alist,clist);
    System.out.println ("has dups? " + hasduplicateList (llist1));
    System.out.println ("has dups? " + hasduplicateList (llist2));
}

输出:

has dups? true
has dups? false