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Java-based LeetCode algorithm problem solutions, regularly updated

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package g1301_1400.s1399_count_largest_group;

// #Easy #Hash_Table #Math #2022_03_17_Time_3_ms_(98.21%)_Space_40.9_MB_(60.71%)

/**
 * 1399 - Count Largest Group\.
 *
 * Easy
 *
 * 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 <= 10⁴
**/
public 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;
    }
}