File: maximum-ascending-subarray-sum/solution.py

Date: 2026-06-06

Time: 17:34

maximum-ascending-subarray-sum/solution.py

Purpose

Solves LeetCode 1800 — Maximum Ascending Subarray Sum. Given an array of positive integers, find the contiguous subarray where every element is strictly greater than the previous one, and return the maximum sum among all such subarrays.

Key Components

concatenated_binary(nums: List[int]) -> int — The sole public function. The name is a copy-paste artifact; it has nothing to do with binary concatenation. The docstring correctly describes the actual behavior: finding the maximum ascending subarray sum.

Contract: nums must be non-empty (the function unconditionally indexes nums[0] on the first line of the body). Elements should be positive integers per the LeetCode constraints.

Patterns

Single-pass greedy accumulation. The algorithm maintains two variables:

• current_sum: the sum of the ascending subarray ending at the current index
• max_sum: the best sum seen so far

At each step, if the current element continues the ascending run (nums[i] > nums[i-1]), it extends the running sum. Otherwise, it resets current_sum to the current element — starting a new candidate subarray. This is the canonical O(n) approach for contiguous subarray problems with a local reset condition, similar in structure to Kadane's algorithm.

Dependencies

Imports: Only typing.List — no external or project-internal dependencies.

Imported by: The test_solution.py in the same directory imports this function. The large "Imported By" list in the prompt is misleading — those are unrelated test files across the repo, likely an artifact of the analysis tool matching on a shared import pattern rather than actual cross-problem imports.

Flow

1. Initialize both maxsum and currentsum to nums[0].

2. Iterate from index 1 to end.

3. If nums[i] > nums[i-1]: accumulate into current_sum.

4. Else: reset current_sum = nums[i] (new ascending run starts).

5. Update max_sum after each step.

6. Return max_sum.

Time: O(n). Space: O(1).

Invariants

• Strict ascent: the condition is >, not >=. Equal adjacent elements break the run — this matches the LeetCode problem specification.
• Reset to current element, not to zero — because the current element is always the start of the next potential ascending subarray.
• maxsum >= currentsum holds after every iteration due to the max() update.

Error Handling

None. An empty nums list will raise IndexError on nums[0]. This is acceptable given LeetCode's constraint that 1 <= nums.length.