# Solving Leetcode Interviews in Seconds with AI: Count Largest Group


	# Introduction
	In this blog post, we will explore how to solve the LeetCode problem "1399" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like [Chatmagic](https://www.chatmagic.app), we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

	# Problem Statement
	> 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  

	# Explanation
	Here's the solution approach, complexity analysis, and Python code:

*   **Digit Sum Calculation:** Calculate the sum of digits for each number from 1 to `n`.
*   **Group Counting:** Use a dictionary (or array if the digit sum range is known and small) to count the frequency of each digit sum.
*   **Maximum Frequency Analysis:** Determine the maximum frequency among all digit sum counts and return the number of digit sums that have this maximum frequency.

*   **Runtime Complexity:** O(n), where n is the input number.
*   **Storage Complexity:** O(1) - The number of unique digit sums is bounded by the constraints. (Technically O(log n) because the digit sum grows logarithmically with n, but because the problem constrains n to be <= 10^4, we can say that the storage is constant since the max digit sum is 36.
)

	
	# Code
	```python
	def countLargestGroup(n: int) -> int:
    """
    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.
    """
    digit_sums = {}
    for i in range(1, n + 1):
        digit_sum = 0
        num = i
        while num > 0:
            digit_sum += num % 10
            num //= 10
        
        if digit_sum in digit_sums:
            digit_sums[digit_sum] += 1
        else:
            digit_sums[digit_sum] = 1
    
    max_frequency = 0
    for digit_sum in digit_sums:
        max_frequency = max(max_frequency, digit_sums[digit_sum])
    
    count = 0
    for digit_sum in digit_sums:
        if digit_sums[digit_sum] == max_frequency:
            count += 1
    
    return count
	```