Stream Practice: Collections & Numbers

Convert the second list to a HashSet for O(1) lookups, then filter the first list with set::contains and apply distinct() to remove duplicates.

Stream the map's entrySet, sort by key or value, and collect to a LinkedHashMap with the four-argument toMap to preserve the sorted order.

Use distinct() to remove duplicate values, sorted(reverseOrder()) for descending order, skip(1) to pass the largest, and findFirst() to get the second-largest.

Use chars().map(Character::toUpperCase).mapToObj(c -> String.valueOf((char) c)).collect(joining()) for character-by-character conversion, or simply str.toUpperCase() in production.

Use filter(Objects::nonNull) to remove nulls, then filter(Predicate.not(String::isBlank)) to remove empty and whitespace-only strings, in that order.

Use two pointers (left and right) that swap elements and move inward for in-place O(1) space reversal, or use IntStream index mapping for a new reversed array.

Use two pointers: slow advances one node per step, fast advances two nodes. When fast reaches the end, slow is at the middle.

List.remove(int) removes by index, List.remove(Object) removes by value. When the argument is a primitive int, Java picks the index overload, causing unexpected behavior with numeric wrapper lists.

distinct().sorted(Comparator.reverseOrder()).skip(1).findFirst() returns the second-largest distinct number as an Optional.

distinct().sorted().skip(1).findFirst() returns the second-smallest distinct number by sorting ascending and skipping the minimum.

Intersection filters one list by membership in a HashSet of the other; union concatenates both and applies distinct.