Longest Subarray With Sum ≤ K

Classic two-pointer / sliding-window: given an array of non-negative integers and a bound K, return the length of the longest contiguous subarray whose sum does not exceed K. Requirements Input: an integer array arr and an integer k. Return: the length of the longest contiguous subarray with sum ≤ k. The common variant assumes non-negative values; the canonical two-pointer solution depends on that assumption. public static int longestSubarray(int[] arr, int k) Notes Standard expanding / contracting window: advance right; whenever the running sum exceeds k, advance left until it doesn't. O(n) time, O(1) space. If the array can contain negative numbers, two pointers no longer work — switch to prefix sums + sorted structure (or monotonic deque) for the general form. Be ready to flag this distinction; Goldman interviewers occasionally probe whether candidates recognize the assumption. Edge cases: k < arr[0] and all elements positive → result is 0 (no single element fits) or 1 (smallest element fits), depending on the problem's exact wording; clarify before coding. Preparation Implement the two-pointer form, then write out the prefix-sum + sorted-set generalization on paper — interviewers like to see candidates state when their primary approach breaks. Closely related: LC 209 "Minimum Size Subarray Sum" (sum ≥ target) and LC 862 "Shortest Subarray with Sum at Least K" (negative-allowed variant).