Date: 2026-06-06
Time: 18:06
monotonic-array/solution.pyThis file solves LeetCode 896 — Monotonic Array. It determines whether a given integer array is monotonic, meaning the sequence is entirely non-decreasing or entirely non-increasing. This is the sole module for this problem in the repo, following the project's one-solution-per-directory convention.
Solution.isMonotonic(self, nums: List[int]) -> bool — The single method. It takes a list of integers and returns True if the array is monotonically non-decreasing, monotonically non-increasing, or both (i.e., all elements equal).
The method uses two boolean flags:
increasing — stays True as long as no pair nums[i] > nums[i+1] is found (non-decreasing property holds).decreasing — stays True as long as no pair nums[i] < nums[i+1] is found (non-increasing property holds).The final return is increasing or decreasing. If either flag survived the full scan, the array is monotonic.
Dual-flag single-pass scan. Rather than making two passes (one checking non-decreasing, one checking non-increasing) or sorting/comparing, this tracks both properties simultaneously in O(n) time and O(1) space. Each adjacent pair can only falsify one of the two flags, so the flags are independently flipped. This is the canonical approach for this problem.
LeetCode Solution class convention. The method lives on a Solution class with no _init_, matching the LeetCode submission interface that the test harness instantiates.
Imports: typing.List — used only for the type annotation on nums.
Imported by: monotonic-array/test_solution.py directly. The massive "Imported By" list in the prompt is an artifact of the repo's shared test infrastructure, not actual imports of this module — each test file imports its own Solution from its sibling solution.py.
1. Initialize increasing = True, decreasing = True.
2. Iterate i from 0 to len(nums) - 2.
3. For each adjacent pair (nums[i], nums[i+1]):
nums[i] > nums[i+1], the sequence is not non-decreasing → set increasing = False.nums[i] < nums[i+1], the sequence is not non-increasing → set decreasing = False.4. Return increasing or decreasing.
For a constant array like [3, 3, 3], neither condition fires, so both flags remain True — correctly returns True.
False by index 2, the loop runs to completion. This is a minor inefficiency but keeps the code simple.True (vacuously monotonic), which is correct per the problem constraints.None. The method assumes valid input per the LeetCode contract (a list of integers with 1 <= len(nums) <= 10^5). No bounds checking, no exception handling, no edge-case guards beyond the natural behavior of range(0) for single-element inputs.