LeetCode/java/hand-of-straights.java

import java.util.TreeMap;

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

    TreeMap<Integer, Integer> cards = new TreeMap<>();
    for (int card : hand) {
      cards.compute(card, (c, present) -> 1 + ((present == null) ? 0 : present));
    }

    while (!cards.isEmpty()) {
      int card = cards.entrySet().iterator().next().getKey();

      for (int i = 0; i < groupSize; ++i) {
        // card doesn't exist
        if (!cards.containsKey(card + i)) {
          return false;
        }

        cards.put(card + i, cards.get(card + i) - 1);

        // remove entry of used cards
        if (cards.get(card + i) == 0) {
          cards.remove(card + i);
        }
      }
    }

    return true;
  }
}