Remove duplicate elements across multiple lists java 8

Question

I have three lists of strings. Now I need to make sure that an element is present in only one of those three list. I don't want to have duplicates across the lists. You can assume that there are no duplicates within each list.

I tried to use the removeIf() and its serving my purpose. Im sure that is not the best way to do it. Is there any other way to do it in Java 8+?

The Priority for the lists is list1 > list2 > list3

List<String> list1 = Stream.of("23","45","655","43","199").collect(Collectors.toList());
List<String> list2 = Stream.of("13","23","54","655","111","13").collect(Collectors.toList());
List<String> list3 = Stream.of("76","45","33","67","43","13").collect(Collectors.toList());

list2.removeIf(i->list1.contains(i));
list3.removeIf(i->list1.contains(i) || list2.contains(i));

System.out.println(list1);
System.out.println(list2);
System.out.println(list3);

The output is below which is expected

[23, 45, 655, 43, 199]
[13, 54, 111, 13]
[76, 33, 67]

list2.removeAll(list1); for the first step would be neat. Also, if you have used Set instead of a list, the complexity would have been O(n) for each step. for lists it is O(n^2) — Gautham M
– Gautham M, Commented May 14, 2021 at 11:11

Ryuzaki L · Accepted Answer · 2021-05-13 18:49:19Z

7

I will recommend to use Set instead of List since Set is of O(1) time complexity

 List<String> list1 = Stream.of("23","45","655","43","199").collect(Collectors.toList());
 List<String> list2 = Stream.of("13","23","54","655","111","13").collect(Collectors.toList());
 List<String> list3 = Stream.of("76","45","33","67","43","13").collect(Collectors.toList());

And then just stream all there by combining and just collect distinct elements into corresponding lists using Collectors.groupingBy

Collection<List<String>> result = Stream.of(list1,list2,list3)
            .flatMap(List::stream)
            .distinct()
            .collect(Collectors.groupingBy(v->list1.contains(v) ? 0 : (list2.contains(v) ? 1 : 2))).values();

    System.out.println(result);  //[[23, 45, 655, 43, 199], [13, 54, 111], [76, 33, 67]]

edited May 13, 2021 at 18:49

answered May 13, 2021 at 18:43

Ryuzaki L

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1 Comment

Harshal Parekh Over a year ago

Quite complicated, but you did it one line.

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