<p>You are given an integer <code>n</code>.</p>

<p>Each number from <code>1</code> to <code>n</code> is grouped according to the sum of its digits.</p>

<p>Return <em>the number of groups that have the largest size</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> n = 13
<strong>Output:</strong> 4
<strong>Explanation:</strong> 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.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> n = 2
<strong>Output:</strong> 2
<strong>Explanation:</strong> There are 2 groups [1], [2] of size 1.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= n &lt;= 10<sup>4</sup></code></li>
</ul>

class Solution {
public:
    int countLargestGroup(int n) {
        if (n < 10) {
            return n;
        }

        int largest_size = 0;

        map<int, int> m; // map sum to num_groups with that sum

        for (int i = 1; i <= n; ++i) {
            string s = to_string(i);
            int sum = 0;
            for (int j = 0; j < s.size(); ++j) {
                sum += (s[j] - '0');
            }

            m[sum]++;
            if (m[sum] > largest_size) {
                largest_size = m[sum];
            }
        }

        int num_groups = 0;

        for (auto it = m.begin(); it != m.end(); ++it) {
            if (it->second == largest_size) {
                num_groups++;
            }
        }

        return num_groups;
    }
};
11000