1399. Count Largest Group

Problem

You are given an integer n.

Each number from 1 to n is grouped according to the sum of its digits.

Return the number of groups that have the largest size.

  Example 1:

Input: n = 13
Output: 4
Explanation: There are 9 groups in total, they are grouped according sum of its digits of numbers from 1 to 13:
[1,10], [2,11], [3,12], [4,13], [5], [6], [7], [8], [9].
There are 4 groups with largest size.

Example 2:

Input: n = 2
Output: 2
Explanation: There are 2 groups [1], [2] of size 1.

  Constraints:

• 1 <= n <= 10^4

Solution (Java)

class Solution {
    public int countLargestGroup(int n) {
        int largest = 0;
        int[] map = new int[37];
        int sumOfDigit = 0;
        for (int i = 1; i <= n; i++) {
            if (i % 10 == 0) {
                // reset and start a new sum
                sumOfDigit = getSumOfDigits(i);
            } else {
                sumOfDigit++;
            }
            int val = ++map[sumOfDigit];
            largest = val > largest ? val : largest;
        }
        return countLargestGroup(largest, map);
    }

    private int countLargestGroup(int largest, int[] arr) {
        int count = 0;
        for (int val : arr) {
            if (val == largest) {
                count++;
            }
        }
        return count;
    }

    private int getSumOfDigits(int num) {
        int sum = 0;
        while (num > 0) {
            sum += num % 10;
            num /= 10;
        }
        return sum;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).