Interval Class: Overlap and Union

/*
 * Problem : Run the commands.
 * Input   : Command lines.
 * Output  : One line per answer.
 * Approach: Interval class
 * Time    : O(n)
 * Space   : O(n)
 * Java    : 8 or newer.
 */
import java.util.Scanner;

public class Main {
        // Step 1: An Interval keeps its two ends and hides them. The overlap rule is written once, here.
        static class Interval {
            private final long low;
            private final long high;

            Interval(long low, long high) {
                this.low = low;
                this.high = high;
            }

            long length() {
                return high - low;
            }

            // Step 2: Two closed intervals overlap when each starts before the other one ends.
            boolean overlaps(Interval other) {
                return low <= other.high && other.low <= high;
            }

            // Step 3: The union of two overlapping intervals runs from the smaller low to the larger high.
            Interval union(Interval other) {
                return new Interval(Math.min(low, other.low), Math.max(high, other.high));
            }

            String text() {
                return low + " " + high;
            }
        }

    // This method solves the task. It receives the input and returns the answer.
    static String[] solve(String[] lines) {
        java.util.Map<String, Interval> named = new java.util.HashMap<String, Interval>();
        java.util.List<String> out = new java.util.ArrayList<String>();
        for (String line : lines) {
            String[] part = line.split(" ");
            if (part[0].equals("make")) {
                named.put(part[1], new Interval(Long.parseLong(part[2]), Long.parseLong(part[3])));
            } else if (part[0].equals("length")) {
                out.add(String.valueOf(named.get(part[1]).length()));
            } else {
                Interval first = named.get(part[1]);
                Interval second = named.get(part[2]);
                if (part[0].equals("overlaps")) {
                    out.add(String.valueOf(first.overlaps(second)));
                } else {
                    out.add(first.overlaps(second) ? first.union(second).text() : "none");
                }
            }
        }
        return out.toArray(new String[0]);
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        java.util.List<String> all = new java.util.ArrayList<>();
        while (scanner.hasNextLine()) {
            String line = scanner.nextLine().trim();
            if (!line.isEmpty()) {
                all.add(line);
            }
        }
        String[] lines = all.toArray(new String[0]);
        System.out.println(String.join("\n", solve(lines)));
    }
}