1742. Maximum Number of Balls in a Box

You are working in a ball factory where you have n balls numbered from lowLimit up to highLimit inclusive (i.e., n == highLimit - lowLimit + 1), and an infinite number of boxes numbered from 1 to infinity.

Your job at this factory is to put each ball in the box with a number equal to the sum of digits of the ball’s number. For example, the ball number 321 will be put in the box number 3 + 2 + 1 = 6 and the ball number 10 will be put in the box number 1 + 0 = 1.

Given two integers lowLimit and highLimit, return the number of balls in the box with the most balls.

class Solution {
    int d(int x) {
        int res = 0;
        while(x) {
            res += x % 10; x /= 10;
        }
        return res;
    }
public:
    int countBalls(int lowLimit, int highLimit) {
        int res = 0;
        vector<int> buc(55);
        for(int i = lowLimit; i <= highLimit; i++) {
            res = max(res, ++buc[d(i)]);
        }
        return res;
    }
};