846. Hand of Straights

class Solution {
    public boolean isNStraightHand(int[] hand, int groupSize) {
        if (hand.length % groupSize != 0) {
            return false;
        }

        TreeMap<Integer, Integer> countMap = new TreeMap<>();
        for (int h : hand) {
            countMap.put(h, countMap.getOrDefault(h, 0) + 1);
        }
        while (!countMap.isEmpty()) {
            int start = countMap.firstKey();
            for (int i = 0; i < groupSize; i++) {
                int value = start + i;
                Integer count = countMap.get(value);
                if (count == null) {
                    return false;
                } else {
                    if (count == 1) {
                        countMap.remove(value);
                    } else {
                        countMap.put(value, count - 1);
                    }
                }
            }
        }

        return true;
    }
}

References

846. Hand of Straights
1296. Divide Array in Sets of K Consecutive Numbers