Simple example
Input
arr = [1, 2, 3, 4, 5], K = 10
Output
4
The subarray [1,2,3,4] has sum 10 and length 4, which is the longest with sum <= 10.
Full lesson preview
Find the longest subarray with sum at most K
Given a non-negative integer array and a target K, find the length of the longest contiguous subarray whose sum is <= K using sliding window.
Python practice16 minTwo Pointers & Sliding WindowIntermediateLast updated March 26, 2026
Problem statement
Given an array of non-negative integers arr and an integer K, return the length of the longest contiguous subarray whose sum is less than or equal to K. If no such subarray exists, return 0. Because all numbers are non-negative, a sliding window (two-pointer) approach can be used to maintain subarray sum efficiently.
Task
Implement an O(n) sliding window solution that returns the length of the longest contiguous subarray with sum at most K.
Examples
Input format
Two inputs: a list of non-negative integers arr and an integer K.
Output format
An integer representing the length of the longest contiguous subarray with sum <= K.
Constraints
0 <= len(arr) <= 10^5; 0 <= arr[i] <= 10^9; 0 <= K <= 10^18. Expected time: O(n), extra space: O(1).
Samples
Sample 1
Input
[3,1,2,1,1], 4
Output
3
Subarray [1,2,1] has sum 4 and length 3.