Java 8 threads, how to find the minimum difference between elements from 2 lists

Question

I am completely new to Streams Java 8and currently trying to solve this problem, I have two lists:

List<Integer> list1 = Arrays.asList(5, 11,17,123);
List<Integer> list2 = Arrays.asList(124,14,80);

I want to find the absolute minimum difference that exists between all the elements from these lists.

Expected Result: 1(124-123=1)

Not a problem to implement it with Java 7, but how can I achieve this with Streams Java8? How can I repeat an element forEachfrom List1as well as forEachfrom List2and save the value of min?

Answer 1

Try this one

public static void main(String[] args) {
        List<Integer> list1 = Arrays.asList(5, 11,17,123); 
        List<Integer> list2 = Arrays.asList(124,14,80);
        OptionalInt min = list1.stream()
                          .flatMap(n -> list2.stream()
                          .map(r -> n-r > 0? n-r: r-n))
                          .mapToInt(t -> t).min();
        System.out.println(min.getAsInt());
    }

Edit (Holger's suggestion)

 OptionalLong min = list1.stream()
.flatMapToLong(n -> list2.stream()
.mapToLong(r -> Math.abs(r-(long)n))).min();

Answer 2

" 1 2" Stream API, , . , n × m.

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, :

public static long smallestDistance(List<Integer> list1, List<Integer> list2) {
    int[] list2Sorted = list2.stream().mapToInt(Integer::intValue).sorted().toArray();
    if(list2Sorted.length == 0) throw new IllegalArgumentException("list2 is empty");
    long smallest = Long.MAX_VALUE;
    for(int i: list1) {
        int pos = Arrays.binarySearch(list2Sorted, i);
        if(pos >= 0) return 0;
        pos ^= -1;
        if(pos < list2Sorted.length) {
            long d = Math.abs(list2Sorted[pos] - (long)i);
            if(d < smallest) smallest = d;
        }
        if(pos > 0) {
            long d = Math.abs(list2Sorted[pos-1] - (long)i);
            if(d < smallest) smallest = d;
        }
    }
    if(smallest == Long.MAX_VALUE) throw new IllegalArgumentException("list1 is empty");
    return smallest;
}

, . , O(n×m) ( ) O((n+m)×log(m)) ( ). , , .

, :

List<Integer> list1
    = IntStream.range(0, 100000).mapToObj(i -> i*2).collect(Collectors.toList());
List<Integer> list2
    = IntStream.range(0, 100000).mapToObj(i -> i*2+1).collect(Collectors.toList());

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