Is Digit Frequency Score easy or hard?

Digit Frequency Score is generally classified as an easy problem. The core requirement is recognizing that counting digit occurrences simplifies the task. Once frequencies are stored, computing the final score becomes a straightforward constant-time operation.

Digit Frequency Score Python/Java solution

Most implementations iterate through the string and increment a counter for each digit. In Python, a list of size 10 or collections.Counter can be used. In Java, an int[10] array is common. Both versions run in O(n) time and constant extra space when using the fixed array.

How to solve Digit Frequency Score in O(n)?

Scan the digit string once and maintain a frequency array of length 10. For each character, convert it to its numeric value and increment the corresponding index. After counting all digits, apply the scoring rule using the stored frequencies. This single-pass counting strategy guarantees O(n) runtime.

What is the best approach for Digit Frequency Score?

The most efficient solution counts digit occurrences using a fixed array of size 10. Each digit from the input is processed once and its counter is incremented. After building the frequency table, the score is computed directly from those counts. This runs in O(n) time with O(1) extra space.

Is Digit Frequency Score asked at Google/Amazon/Meta?

Frequency counting problems appear frequently in technical interviews at large companies including Google, Amazon, and Meta. Variants often involve counting characters, digits, or elements and deriving a value from those counts. The core technique—efficient counting with arrays or hash maps—is widely tested.

What data structure is used in Digit Frequency Score?

The problem is typically solved with either a hash map or a fixed-size integer array. Because digits range from 0 to 9, a simple array of size 10 is usually preferred. This provides constant-time updates and avoids the overhead of hashing.

What is the time complexity of Digit Frequency Score?

The optimal implementation runs in O(n) time where n is the number of digits in the input. Each digit is processed exactly once during frequency counting. A small constant pass over the 10-digit frequency array may follow, which does not affect the linear complexity.

3945. Digit Frequency Score - Practice Online

You are given an integer n.

The score of n is defined as the sum of d * freq(d) over all distinct digits d, where freq(d) denotes the number of times the digit d appears in n.

Return an integer denoting the score of n.

Example 1:

Input: n = 122

Output: 5

Explanation:

The digit 1 appears 1 time, contributing 1 * 1 = 1.
The digit 2 appears 2 times, contributing 2 * 2 = 4.
Thus, the score of n is 1 + 4 = 5.

Example 2:

Input: n = 101

Output: 2

Explanation:

The digit 0 appears 1 time, contributing 0 * 1 = 0.
The digit 1 appears 2 times, contributing 1 * 2 = 2.
Thus, the score of n is 2.

Constraints:

1 <= n <= 10⁹