CodeWars/4kyu/sum_of_intervals/solution.java

package cw;

import java.util.TreeSet;

class Interval {
    private static class Range implements Comparable<Range> {
        private int from;
        private int to;

        public Range(int from, int to) {
            this.from = from;
            this.to = to;
        }

        public int length() {
            return to - from;
        }

        public Range merge(Range other) {
            return new Range(Math.min(from, other.from), Math.max(to, other.to));
        }

        public boolean mergeInSitu(Range other) {
            if (!canMerge(other)) {
                return false;
            }

            from = Math.min(from, other.from);
            to = Math.max(to, other.to);
            return true;
        }

        public boolean has(int x) {
            return from <= x && x <= to;
        }

        public boolean isSubrangeOf(Range other) {
            return other.has(from) && other.has(to);
        }

        public boolean isPrefixOf(Range other) {
            return from <= other.from && other.has(to);
        }

        public boolean isSuffixOf(Range other) {
            return to >= other.to && has(other.from);
        }

        public boolean canMerge(Range other) {
            return isSubrangeOf(other) || isPrefixOf(other) || isSuffixOf(other);
        }

        @Override
        public int compareTo(Range other) {
            if (other == null) {
                throw new NullPointerException();
            }

            if (from == other.from && to == other.to) {
                return 0;
            }

            if (to < other.from || from < other.from) {
                return -1;
            }

            return 1;
        }
    }

    private static void insertRange(TreeSet<Range> ranges, Range range) {
        for (Range r : ranges) {
            if (r.canMerge(range)) {
                ranges.remove(r);
                ranges.add(r.merge(range));
                return;
            }
        }

        ranges.add(range);
    }

    private static boolean mergeRanges(TreeSet<Range> ranges) {
        for (Range x : ranges) {
            for (Range y : ranges) {
                if (x == y) {
                    continue;
                }

                if (x.canMerge(y)) {
                    ranges.remove(x);
                    ranges.remove(y);
                    ranges.add(x.merge(y));
                    return true;
                }
            }
        }

        return false;
    }

    public static int sumIntervals(int[][] intervals) {
        if (intervals == null) {
            return 0;
        }

        TreeSet<Range> ranges = new TreeSet<>();

        // Go through the intervals and construct a set out of them
        // when adding each interval, try to merge it in-situ with any of the
        // existing intervals
        for (int[] interval : intervals) {
            insertRange(ranges, new Range(interval[0], interval[1]));
        }

        // then iteratively merge the set of intervals while possible
        boolean hasChanged = true;
        while (hasChanged) {
            hasChanged = mergeRanges(ranges);
        }

        for (Range r : ranges) {
            System.out.format("%d, %d; ", r.from, r.to);
        }
        System.out.println();

        return ranges.stream().map(Range::length).reduce(Integer::sum).orElse(0);
    }

    public static void main(String[] args) {
        // null argument
        System.out.format("%d == %d\n", Interval.sumIntervals(null), 0);  // => 0

        // empty intervals
        System.out.format("%d == %d\n", Interval.sumIntervals(new int[][]{}), 0);  // => 0
        System.out.format("%d == %d\n", Interval.sumIntervals(new int[][]{{2,2}, {5,5}}), 0);  // => 0

        // disjoined intervals
        System.out.format("%d == %d\n", Interval.sumIntervals(new int[][]{
          {1,2},{3,5}
        }), 3);  // => (2-1) + (5-3) = 3

        // overlapping intervals
        System.out.format("%d == %d\n", Interval.sumIntervals(new int[][]{
          {1,4},{3,6},{2,8}
        }), 7);  // [1,8] => 7
    }
}