在Java中的两个列表中找到第一个列表中的唯一元素

Question

I am trying to find unique elements in a main list by comparing it with another list with a time complexity better than O(mn). Ex:-

listA, listB . I want to get unique elements only in listA and add to a new list.

Here is what I did

for (String item : listA) {
 if (!listB.contains(item)) {
   newList.add(item)
 }
}

Here the time complexity is O(mn). Can anyone help me get to a better solution?

Answer 1

Set<String> setB = new HashSet<>(listB);
for (String item : listA) {
 if (!setB.contains(item)) {
    newList.add(item);
 }
}

Like @Andy Turner suggested. Here , Set.contains Time Complexity is O(1).