Take While and Drop While

/*
 * Problem : Split a prefix.
 * Input   : n, the array, then k.
 * Output  : Two lines.
 * Approach: Stop at the first match.
 * Time    : O(n)
 * Space   : O(n)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
    // This method solves the task. It receives the input and returns the answer.
    static String[] solve(int[] a, int k) {
        // Step 1: Find the first position that is NOT smaller than k. A stream stops at the first match (findFirst).
        int split = java.util.stream.IntStream.range(0, a.length).filter(i -> a[i] >= k).findFirst().orElse(a.length);
        // Step 2: Everything before the split is the "take while" part. Everything from the split is the "drop while" rest.
        String taken = java.util.Arrays.stream(a, 0, split).mapToObj(String::valueOf).collect(java.util.stream.Collectors.joining(" "));
        String rest = java.util.Arrays.stream(a, split, a.length).mapToObj(String::valueOf).collect(java.util.stream.Collectors.joining(" "));
        return new String[] {taken.isEmpty() ? "empty" : taken, rest.isEmpty() ? "empty" : rest};
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int size = scanner.nextInt();
        int[] a = new int[size];
        for (int i = 0; i < size; i++) {
            a[i] = scanner.nextInt();
        }
        int k = scanner.nextInt();
        System.out.println(String.join("\n", solve(a, k)));
    }
}