Basic example
Input
find_max([3, 1, 4, 2])
Output
4
Among the numbers 3, 1, 4, 2 the largest is 4.
Full lesson preview
Find Maximum Value
Find the largest number in a list of integers. Returns None for an empty list.
Python practice6 minLoops & IterationBeginnerLast updated March 15, 2026
Problem statement
Write a function find_max(nums) that takes a list of integers nums and returns the maximum value in the list. If nums is empty, return None. Do not use the built-in max() function; iterate through the list and track the largest value manually.
Task
Practice iterating through a list to identify the maximum value and handle empty inputs.
Examples
Input format
A single list of integers, e.g. [1, 2, 3].
Output format
An integer (the maximum) or None for an empty list.
Constraints
You must not use the built-in max() or sorted(). Aim for O(n) time and O(1) extra space.
Samples
Sample 1
Input
find_max([-5, -2, -3])
Output
-2
The maximum among the negatives is -2.