Is Minimum Number of Groups to Create a Valid Assignment easy or hard?

The problem is rated Medium on LeetCode with an acceptance rate around 25%. The challenge comes from recognizing that the array itself is not important after counting frequencies. The real task is validating whether frequencies can be partitioned into nearly equal group sizes using a greedy check.

Minimum Number of Groups to Create a Valid Assignment Python/Java solution

Python and Java implementations typically start with a dictionary or HashMap to count frequencies. Then they iterate possible base group sizes and compute the number of groups needed using integer division and remainder checks. The logic is identical across languages, with differences only in syntax.

How to solve Minimum Number of Groups to Create a Valid Assignment in O(n)?

First build a frequency map of all values in the array. Determine the minimum frequency and iterate possible base group sizes from that value downward. For each candidate size k, verify that every frequency f can be split into groups of size k or k+1 using division checks. Once a valid configuration is found, sum the number of groups for all frequencies.

What is the best approach for Minimum Number of Groups to Create a Valid Assignment?

The greedy frequency distribution approach is typically the best solution. Count occurrences of each number with a hash map, then test feasible base group sizes derived from the minimum frequency. For each candidate size k, check whether every frequency can be split into groups of size k or k+1. This minimizes the total number of groups while keeping group sizes balanced.

Is Minimum Number of Groups to Create a Valid Assignment asked at Google/Amazon/Meta?

Problems involving frequency grouping and greedy distribution frequently appear in interviews at companies like Google, Amazon, and Meta. This specific LeetCode problem tests reasoning about constraints, counting with hash maps, and greedy validation, which are common interview patterns.

What data structure is used in Minimum Number of Groups to Create a Valid Assignment?

The core data structure is a hash map that stores the frequency of each value in the array. After counting, the algorithm iterates over these frequencies and applies greedy arithmetic checks to determine how many groups are needed for each value.

What is the time complexity of Minimum Number of Groups to Create a Valid Assignment?

The overall time complexity is roughly O(n + m * k), where n is the array length, m is the number of distinct values, and k is the number of candidate group sizes tested. Frequency counting takes O(n), and validation across frequencies is usually small in practice, making the solution close to linear time.

Description Hints 6 Solution Video 10:35

2910. Minimum Number of Groups to Create a Valid Assignment

Medium25.0% acceptance1 company

You are given a collection of numbered balls and instructed to sort them into boxes for a nearly balanced distribution. There are two rules you must follow:

Balls with the same box must have the same value. But, if you have more than one ball with the same number, you can put them in different boxes.
The biggest box can only have one more ball than the smallest box.

Return the fewest number of boxes to sort these balls following these rules.

Example 1:

Input: balls = [3,2,3,2,3]

Output: 2

Explanation:

We can sort balls into boxes as follows:

[3,3,3]
[2,2]

The size difference between the two boxes doesn't exceed one.

Example 2:

Input: balls = [10,10,10,3,1,1]

Output: 4

Explanation:

We can sort balls into boxes as follows:

[10]
[10,10]
[3]
[1,1]

You can't use fewer than four boxes while still following the rules. For example, putting all three balls numbered 10 in one box would break the rule about the maximum size difference between boxes.

Constraints:

1 <= nums.length <= 10⁵
1 <= nums[i] <= 10⁹

Asked at 1 company

Amazon

Topics

Hints open one at a time

Hint 1

Calculate the frequency of each number.

Hint 2

For each x in the range [1, minimum_frequency], try to create groups with either x or x + 1 indices assigned to them while minimizing the total number of groups.

Hint 3

For each distinct number, using its frequency, check that all its occurrences can be assigned to groups of size x or x + 1 while minimizing the number of groups used.

Hint 4

To get the minimum number of groups needed for a number having frequency f to be assigned to groups of size x or x + 1, let a = f / (x + 1) and b = f % (x + 1).

If b == 0, then we can simply create a groups of size x + 1.
If x - b <= a, we can have a - (x - b) groups of size x + 1 and x - b + 1 groups of size x. So, in total, we have a + 1 groups.
Otherwise, it's impossible.

Hint 5

The minimum number of groups needed for some x is the total minimized number of groups needed for each distinct number.

Hint 6

The answer is the minimum number of groups needed for each x in the range [1, minimum_frequency].

10:35

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1class Solution:
2    def minGroupsForValidAssignment(self, balls: List[int]) -> int:
3        

Starter codePython 3Spaces: 4

Examples

Case 1

Input

[3,2,3,2,3]

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