Basic example
Input
nums = [1, 2, 3, 4, 5], k = 7
Output
3
The longest subarray with sum <= 7 is [1,2,3] with length 3 (sum=6).
Full lesson preview
Find the longest subarray with sum at most k
Given a list of non-negative integers and a threshold k, find the maximum length of a contiguous subarray whose sum is <= k.
Python practice14 minArrays – Fundamentals & PatternsIntermediateLast updated March 25, 2026
Problem statement
You are given an array of non-negative integers nums and an integer k. Return the length of the longest contiguous subarray whose sum is less than or equal to k.
Because all numbers are non-negative, a sliding-window (two-pointer) approach can be used to expand and contract a window while tracking its sum.
If no subarray satisfies the condition, return 0.
Task
Implement an efficient sliding-window algorithm to compute the length of the longest contiguous subarray with sum at most k in O(n) time and O(1) extra space.
Examples
Input format
Function input: longest_subarray_at_most_k(nums, k) where nums is a list of non-negative integers and k is an integer.
Output format
Return an integer representing the maximum length of a contiguous subarray whose sum is <= k.
Constraints
0 <= len(nums) <= 10^5. 0 <= nums[i] <= 10^9. -10^18 <= k <= 10^18. Expected time O(n), extra space O(1).
Samples
Sample 1
Input
nums = [2, 1, 1, 1, 5, 1, 1], k = 4
Output
3
One longest subarray is [1,1,1] with sum 3 and length 3.