remove-covered-intervals-v1.java

class Solution {
    public int removeCoveredIntervals(int[][] intervals) {
        Arrays.sort(intervals, (a, b) -> (a[0] != b[0] ? Integer.compare(a[0], b[0]) : Integer.compare(b[0], a[0])));
        int right = -1;
        int count = 0;
        for (int[] inter : intervals) {
            if (inter[1] > right) {
                count ++;
                right = inter[1];
            }
        }
        return count;
    }
}

remove-covered-intervals-v2.java

class Solution {
    public int removeCoveredIntervals(int[][] intervals) {
        Arrays.sort(intervals, (a, b) -> (Integer.compare(a[0], b[0])));
        int left = -1;
        int right = -1;
        int count  = 0;
        for (int[] inter : intervals) {
            if (inter[0] > left && inter[1] > right) {
                left = inter[0];
                count += 1;
            }
            right = Math.max(right, inter[1]);
        }
        return count;
    }
}

remove-covered-intervals-v3.java

class Solution {
    
    class Point implements Comparable<Point>{
        int[] interval;
        int flag;
        
        public Point(int[] interval, int flag) {
            this.interval = interval;
            this.flag = flag;
        }
        
        @Override
        public int compareTo(Point other) {
            if (this.interval[this.flag] != other.interval[other.flag]) {
                return Integer.compare(this.interval[this.flag], other.interval[other.flag]);
            } else {
                return Integer.compare(other.interval[1- other.flag], this.interval[1- this.flag]);
            }
        }
    }
    
    public int removeCoveredIntervals(int[][] intervals) {
        List<Point> pList = new ArrayList<>();
        for (int[] inter : intervals) {
            pList.add(new Point(inter, 0)); // start
            pList.add(new Point(inter, 1)); // end
        }
        Collections.sort(pList);
        Deque<Point> deque = new ArrayDeque<>();
        
        int n = intervals.length;
        for (Point p : pList) {
            if (p.flag == 0) { // start
                deque.addLast(p);
            } else { // end
                Point first = deque.peekFirst();
                if (p.interval[0] == first.interval[0] && p.interval[1] == first.interval[1]) {
                    while(!deque.isEmpty() && deque.peekFirst().interval[1] <= p.interval[1]) {
                        Point polled = deque.pollFirst();
                    }
                } else if (p.interval[0] >= first.interval[0] && p.interval[1] <= first.interval[1]) {
                    n -= 1;
                } else {
                    // do nothing
                }
            }
        }
        
        return n;
    }
}