Maximum Number of Balls in a Box

给一个上界和下界, 求中间所有数字的数字和的出现次数.

class Solution {
    public int countBalls(int lowLimit, int highLimit) {
        Map<Integer, Integer> map = new HashMap<>();
        for(int i = lowLimit; i <= highLimit; i++) {
            int sum = 0;
            int j = i;
            while(j > 0) {
                sum += (j % 10);
                j /= 10;
            }
            map.put(sum, map.getOrDefault(sum, 0) + 1);
        }
        int max = Integer.MIN_VALUE;
        for(Integer i : map.values()){
            max = Math.max(max, i);
        }
        return max;
    }
}