## Description

https://leetcode.com/problems/count-largest-group/

Given an integer `n`

. Each number from `1`

to `n`

is grouped according to the sum of its digits.

Return how many groups have the largest size.

**Example 1:**

Input:n = 13Output:4Explanation: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 = 2Output:2Explanation:There are 2 groups [1], [2] of size 1.

**Example 3:**

Input:n = 15Output:6

**Example 4:**

Input:n = 24Output:5

**Constraints:**

`1 <= n <= 10^4`

## Explanation

First group numbers by sum of their digits. And then group by the length of the first groups result. Finally find the group with maximum group size.

## Python Solution

```
class Solution:
def countLargestGroup(self, n: int) -> int:
results = []
groups = defaultdict(list)
for i in range(1, n + 1):
i_str = str(i)
sum_digits = 0
for c in i_str:
sum_digits += int(c)
if sum_digits in groups:
groups[sum_digits].append(i)
else:
groups[sum_digits] = [i]
size_groups = {}
max_size = -1
for key, value in groups.items():
max_size = max(max_size, len(value))
size_groups[len(value)] = size_groups.get(len(value), 0) + 1
return size_groups[max_size]
```

- Time Complexity: O(N).
- Space Complexity: O(N).