Merge pull request #15 from codewithme-py/feat/sliding-window-maximum-0239

problem solution & test 0239

Author: codewithme-py

solutions/sliding_window_maximum_0239.py

@@ -0,0 +1,45 @@
+from collections import deque
+
+
+class Solution:
+    def maxSlidingWindow(self, nums: list[int], k: int) -> list[int]:
+        """
+        Finds the maximum values in each sliding window of size k.
+
+        The algorithm uses a monotonic deque (double-ended queue) to achieve
+        a time complexity of O(n), where n is the length of the nums array.
+
+        The monotonic deque stores indices of elements in the nums array in
+        descending order of their values. Thus, the element with index dq[0]
+        is always the index of the maximum element in the current window.
+
+        Args:
+            nums (list[int]): Input array of integers.
+            k (int): Size of the sliding window.
+
+        Returns:
+            list[int]: List of maximum values for each window.
+
+        Example:
+            >>> nums = [1, 3, -1, -3, 5, 3, 6, 7]
+            >>> k = 3
+            >>> Solution().maxSlidingWindow(nums, k)
+            [3, 3, 5, 5, 6, 7]
+
+        Time Complexity:
+            O(n), where n is the length of nums. Each index is added and removed
+            from the deque at most once.
+
+        Space Complexity:
+            O(k), as the deque stores at most k indices.
+        """
+        result, dq = [], deque()
+        for i in range(len(nums)):
+            if dq and dq[0] == i - k:
+                dq.popleft()
+            while dq and nums[dq[-1]] < nums[i]:
+                dq.pop()
+            dq.append(i)
+            if i >= k - 1:
+                result.append(nums[dq[0]])
+        return result

tests/test_sliding_window_maximum_0239.py

@@ -0,0 +1,16 @@
+import pytest
+
+from solutions.sliding_window_maximum_0239 import Solution
+
+
+@pytest.mark.parametrize('nums, k, expected', [
+    ([1,3,-1,-3,5,3,6,7], 3, [3,3,5,5,6,7]),
+    ([1], 1, [1]),
+    ([1, -1], 1, [1, -1]),
+    ([9, 11], 2, [11]),
+    ([4, -2], 2, [4]),
+])
+
+def test_solution(nums: list[int], k: int, expected: list[int]) -> None:
+    sol = Solution()
+    assert sol.maxSlidingWindow(nums, k) == expected