Is Count Largest Group easy or hard?

Count Largest Group is classified as an Easy problem. It mainly tests basic iteration, digit extraction, and frequency counting rather than advanced algorithms.

Count Largest Group Python/Java solution

The typical implementation iterates from 1 to n, computes the digit sum using modulo and division, and updates a counter array or hash map. Python often uses a list or defaultdict, while Java commonly uses an int array or HashMap.

How to solve Count Largest Group in O(n)?

Iterate from 1 to n, compute the digit sum of each number, and increment a counter for that sum. Store counts in a small array indexed by the digit sum. After processing all numbers, scan the array to find the maximum frequency and count how many groups reach it.

What is the best approach for Count Largest Group?

The most efficient approach groups numbers by their digit sum and counts frequencies using a fixed array. Since the digit sum range is small, direct indexing avoids hash map overhead. This gives O(n * d) time, where d is the number of digits, and O(1) extra space.

Is Count Largest Group asked at Google/Amazon/Meta?

Problems involving digit manipulation, grouping, and frequency counting appear frequently in interviews at companies like Amazon and Google. While this exact problem may not always appear, the pattern of grouping elements using a computed key is common.

What data structure is used in Count Largest Group?

The core data structure is a frequency counter indexed by digit sum. This can be implemented with a hash table for flexibility or a fixed-size array for better performance when the range of sums is known.

What is the time complexity of Count Largest Group?

The time complexity is O(n * d) because each number from 1 to n is processed once and computing the digit sum takes d operations. For typical constraints where numbers have at most 4–5 digits, this behaves like O(n).

Description Hints 1 Solution Video 12:05

1399. Count Largest Group

Easy74.7% acceptance5 companies

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

Asked at 5 companies

Mercari

Google Amazon Meta Bloomberg

Topics

Hash Table Math

Hints open one at a time

Hint 1

Count the digit sum for each integer in the range and find out the largest groups.

12:05

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1class Solution:
2    def countLargestGroup(self, n: int) -> int:
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