Data Stream as Disjoint Intervals

Given a data stream input of non-negative integers a1, a2, ..., an, ..., summarize the numbers seen so far as a list of disjoint intervals.

For example, suppose the integers from the data stream are 1, 3, 7, 2, 6, ..., then the summary will be:

[1, 1] [1, 1], [3, 3] [1, 1], [3, 3], [7, 7] [1, 3], [7, 7] [1, 3], [6, 7]

Follow up: What if there are lots of merges and the number of disjoint intervals are small compared to the data stream's size?

Credits:Special thanks to @yunhong for adding this problem and creating most of the test cases.

Solution

/**
 * Definition for an interval.
 * public class Interval {
 *     int start;
 *     int end;
 *     Interval() { start = 0; end = 0; }
 *     Interval(int s, int e) { start = s; end = e; }
 * }
 */
public class SummaryRanges {

 TreeSet<Interval> treeSet;

    public SummaryRanges() {
        treeSet = new TreeSet<>((a, b) -> Integer.compare(a.start, b.start));
    }

    public void addNum(int val) {
        Interval addInterval = new Interval(val, val);
        Interval floor = treeSet.floor(addInterval);
        if (floor != null) {
            if (floor.end >= val) {
                return;
            } else if (floor.end + 1 == val) {
                addInterval.start = floor.start;
                treeSet.remove(floor);
            }
        }

        Interval ceiling = treeSet.higher(addInterval);
        if (ceiling != null && ceiling.start - 1 == val) {
            addInterval.end = ceiling.end;
            treeSet.remove(ceiling);
        }

        treeSet.add(addInterval);
    }

    public List<Interval> getIntervals() {
        return treeSet.stream().collect(Collectors.toList());
    }
}

/**
 * Your SummaryRanges object will be instantiated and called as such:
 * SummaryRanges obj = new SummaryRanges();
 * obj.addNum(val);
 * List<Interval> param_2 = obj.getIntervals();
 */