The Forbidden Ceiling

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
Asked in
Raisin

Problem

Given a non-empty list of integers, return the maximum. You may not use max() or any sort/sorted helper. Runtime must be O(n).

Round up. But not the obvious way.

Example

Input:

nums = [3,1,4,1,5,9,2,6]

Output:

9

Worked solution and explanation

Why this problem exists in real interviews

This tests whether a candidate can implement a basic linear scan without relying on built-in functions. It probes understanding of comparison-based algorithms at the most fundamental level.

Break down the requirements

Step 1: Initialize with the first element

Use the first element as the initial maximum.

Step 2: Scan the rest of the list

Compare each element to the current maximum and update if larger.

The solution

Linear scan maximum
def find_max(nums: list) -> int:
    if not nums:
        return None
    largest = nums[0]
    for i in range(1, len(nums)):
        if nums[i] > largest:
            largest = nums[i]
    return largest

Common follow-up questions