merge.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

public class MergeRangesJava {
    public static class Range {
        public final int start;
        public final int end;

        public Range(int start, int end) {
            this.start = start;
            this.end = end;
        }

        @Override
        public String toString() {
            return "Range{" +
                    "start=" + start +
                    ", end=" + end +
                    '}';
        }
    }

    public static List<Range> merge(Range... ranges) {
        List<Range> sorted = Arrays.asList(ranges);
        sorted.sort((r1, r2) -> Integer.compare(r1.start, r2.start));
        Iterator<Range> it = sorted.iterator();
        if (it.hasNext()) {
            List<Range> result = new ArrayList<>();
            Range current = it.next();
            while (it.hasNext()) {
                Range next = it.next();
                if (current.end >= next.start) {
                    current = new Range(current.start, Math.max(current.end, next.end));
                } else {
                    result.add(current);
                    current = next;
                }
            }
            result.add(current);
            return result;
        } else {
            return Collections.emptyList();
        }
    }

    public static void main(String[] args) {
        System.out.println(merge());
        System.out.println(merge(new Range(1, 1)));
        System.out.println(merge(new Range(1, 1), new Range(1, 1)));
        System.out.println(merge(new Range(1, 2), new Range(2, 3)));
        System.out.println(merge(new Range(1, 5), new Range(2, 3), new Range(6, 7)));
    }
}