Date: 2026-06-06
Time: 16:42
This file solves LeetCode 2395: Find Subarrays With Equal Sum. It determines whether any two distinct length-2 subarrays in an integer array share the same sum. It owns exactly one responsibility: the equalsumsubarrays function, which is the solution entry point imported by the corresponding test file and (based on the imported_by list) referenced broadly across the test suite — likely via a shared test harness pattern.
equalsumsubarrays(nums: list[int]) -> boolContract: Given a list of integers with length >= 2, returns True if there exist two length-2 subarrays starting at different indices whose element sums are equal.
The function uses a single-pass scan with a hash set for O(n) time and O(n) space.
Sliding window + seen-set: Rather than computing all pairwise sums and comparing (O(n^2)), the code slides a width-2 window across the array, computing each sum on the fly. Each sum is checked against a seen set before being added — a standard duplicate-detection idiom. This is the minimal correct approach: no prefix-sum array, no sorting, just a set and one pass.
Early return: The function short-circuits on the first duplicate sum found, avoiding unnecessary work.
Imports: None — pure stdlib Python, no external dependencies.
Imported by: The function is imported by find-subarrays-with-equal-sum/testsolution.py directly. The massive importedby list in the prompt (300+ test files) is an artifact of the repo's test harness structure — those test files likely share a common import mechanism or test runner, not direct imports of this function.
1. Initialize an empty set seen.
2. Iterate i from 0 to len(nums) - 2 (inclusive).
3. Compute s = nums[i] + nums[i + 1] — the sum of the current length-2 subarray.
4. If s is already in seen, return True immediately.
5. Otherwise, add s to seen and continue.
6. If the loop completes without finding a duplicate, return False.
range(len(nums) - 1) guarantees nums[i + 1] is always in bounds.len(nums) >= 2 (stated in docstring, not enforced). With a single-element list, the loop body never executes and the function returns False — safe but semantically meaningless.seen set accumulates sums from prior indices only. The current sum is checked *before* insertion, so a subarray is never compared against itself.None. The function trusts its caller to provide a valid list of integers. An empty list or single-element list silently returns False. Non-integer elements would propagate a TypeError from the + operator — no defensive handling.
find-subarrays-with-equal-sum/test_solution.py — How the test harness exercises this function, including edge casesfind-subarrays-with-equal-sum/review.md — Code review notes that may document alternative approaches or known limitationscontains-duplicate-ii/solution.py:containsNearbyDuplicate — Same seen-set-with-sliding-window pattern applied to a different constraint (index distance)set-based-duplicate-detection — This pattern recurs across many solutions in the repo (e.g., two-sum, contains-duplicate-ii, first-letter-to-appear-twice)equal-sum-subarrays-is-single-pass — equalsumsubarrays visits each element at most once, giving O(n) time complexityequal-sum-subarrays-checks-before-insert — The duplicate check (if s in seen) occurs before seen.add(s), preventing a subarray from matching itselfequal-sum-subarrays-no-validation — The function performs no input validation; it assumes nums has length >= 2 per the docstring contractequal-sum-subarrays-early-return — The function returns True on the first duplicate sum found, not after scanning the entire array