The Tally Counter

An easy Python interview practice problem on DataDriven. Write the Python and run it against test cases, with instant feedback.

Domain

Python

Difficulty

easy

Seniority

L3

Problem

Given a list of integers and a target, return the count of occurrences of target. Do not use list.count().

How many times does a single guest show up to the party?

Example 1

Input:

nums = [1,2,3,2,1], target = 2

Output:

2

Example 2

Input:

nums = [5,5,5], target = 5

Output:

3

Worked solution and explanation

Why this problem exists in real interviews

This tests basic loop mechanics and the ability to implement a trivial built-in from scratch. It probes whether a candidate can write a clean counting loop without relying on list.count().

Break down the requirements

Step 1: Initialize a counter to zero

The counter tracks how many times the target appears.

Step 2: Iterate and compare each element to the target

Increment the counter when a match is found.

The solution

def count_occurrences(nums: list, target: int) -> int:
    count = 0
    for num in nums:
        if num == target:
            count += 1
    result = count
    return result

Common follow-up questions

• What if the list was sorted? Could you do better than O(n)? (Tests binary search for the first and last occurrence, giving O(log n).)
• What if you needed to count multiple targets at once? (Tests using a dict to accumulate counts for each target in one pass.)
• What if elements were floating-point and you needed approximate matching? (Tests using an epsilon tolerance: `abs(num - target) < epsilon`.)