Minimum Operations to Make Character Frequencies Equal Python/Java solution

Most implementations start with a 26-length frequency array, iterate over possible target frequencies, and compute operation costs for each letter. The same logic works in Python, Java, C++, and Go because it relies only on counting and simple arithmetic operations.

What is the best approach for Minimum Operations to Make Character Frequencies Equal?

The most effective approach is to count character frequencies and enumerate a target frequency k. For each possible k, compute the minimum cost to adjust every character count using deletions, insertions, or conversions. This reduces the search space to at most maxFreq candidates and runs in O(26 * maxFreq) time with constant extra space.

Is Minimum Operations to Make Character Frequencies Equal asked at Google/Amazon/Meta?

Hard string optimization problems involving frequency balancing and dynamic programming are common at companies like Google, Amazon, and Meta. This problem tests counting, greedy reasoning, and DP over a small alphabet, patterns frequently seen in senior-level interview rounds.

What data structure is used in Minimum Operations to Make Character Frequencies Equal?

A frequency array or hash table is used to count occurrences of each character. The solution then applies enumeration and sometimes dynamic programming to compute the cheapest sequence of insert, delete, or convert operations.

What is the time complexity of Minimum Operations to Make Character Frequencies Equal?

The optimal solution runs in O(26 * maxFreq) time. You first count the 26 lowercase letter frequencies, then evaluate each possible target frequency up to the maximum count. Space complexity is O(1) because the alphabet size is fixed.

Description Hints 7 Video 42:24

3389. Minimum Operations to Make Character Frequencies Equal

Q: Is Minimum Operations to Make Character Frequencies Equal easy or hard?

LeetCode classifies this problem as Hard with an acceptance rate around 26%. The difficulty comes from recognizing that the final configuration must use a single frequency and efficiently balancing surplus and deficit characters across the alphabet.

Q: How to solve Minimum Operations to Make Character Frequencies Equal in O(n)?

Start by counting character frequencies in O(n). Then enumerate possible target frequencies k and compute the minimum operations using surplus and deficit balancing across characters. Since the alphabet size is fixed (26), the additional work is constant relative to n, giving an effective linear-time solution.

Hard25.8% acceptance2 companies

You are given a string s.

A string t is called good if all characters of t occur the same number of times.

You can perform the following operations any number of times:

Delete a character from s.
Insert a character in s.
Change a character in s to its next letter in the alphabet.

Note that you cannot change 'z' to 'a' using the third operation.

Return the minimum number of operations required to make s good.

Example 1:

Input: s = "acab"

Output: 1

Explanation:

We can make s good by deleting one occurrence of character 'a'.

Example 2:

Input: s = "wddw"

Output: 0

Explanation:

We do not need to perform any operations since s is initially good.

Example 3:

Input: s = "aaabc"

Output: 2

Explanation:

We can make s good by applying these operations:

Change one occurrence of 'a' to 'b'
Insert one occurrence of 'c' into s

Constraints:

3 <= s.length <= 2 * 10⁴
s contains only lowercase English letters.

Asked at 2 companies

Tiktok

Google

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Hints open one at a time

Hint 1

The order of the letters in the string is irrelevant.

Hint 2

Compute an occurrence array occ where occ[x] is the number of occurrences of the x character of the alphabet. How do the described operations change occ?

Hint 3

We have three types of operations: increase any occ[x] by 1, decrease any occ[x] by 1, or decrease any occ[x] by 1 and simultaneously increase occ[x + 1] by 1 at the same time. To make s good, we need to make occ good. occ is good if and only if every occ[x] equals either 0 or some constant c.

Hint 4

If you know the value of c, how can you calculate the minimum operations required to make occ good?

Hint 5

Observation 1: It is never optimal to apply the third type of operation (simultaneous decrease and increase) on two continuous elements occ[x] and occ[x + 1]. Instead, we can decrease occ[x] by 1 then increase occ[x + 2] by 1 to achieve the same effect.

Hint 6

Observation 2: It is never optimal to increase an element of occ then decrease it, or vice versa.

Hint 7

Use dynamic programming where dp[i] is the minimum number of operations required to make occ[0..i] good. You will need to use the above observations to come up with the transitions.

3389. Minimum Operations to Make Character Frequencies Equal

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