TheAlgorithms/Python · error · ValueError

Window size must be a positive integer

Error message

Window size must be a positive integer

What it means

Raised by sliding_window_maximum when window_size is <= 0. The deque-based algorithm assumes each window covers at least one element, so zero or negative window sizes are rejected up front. An empty numbers list is legal and returns [] — only the window size is validated.

Source

Thrown at other/sliding_window_maximum.py:36

        ValueError: If window_size is not a positive integer.

    Time Complexity: O(n) - each element is added and removed at most once
    Space Complexity: O(k) - deque stores at most window_size indices

    Examples:
    >>> sliding_window_maximum([1, 3, -1, -3, 5, 3, 6, 7], 3)
    [3, 3, 5, 5, 6, 7]
    >>> sliding_window_maximum([9, 11], 2)
    [11]
    >>> sliding_window_maximum([], 3)
    []
    >>> sliding_window_maximum([4, 2, 12, 3], 1)
    [4, 2, 12, 3]
    >>> sliding_window_maximum([1], 1)
    [1]
    """
    if window_size <= 0:
        raise ValueError("Window size must be a positive integer")
    if not numbers:
        return []

    result: list[int] = []
    index_deque: deque[int] = deque()

    for current_index, current_value in enumerate(numbers):
        # Remove the element which is out of this window
        if index_deque and index_deque[0] == current_index - window_size:
            index_deque.popleft()

        # Remove useless elements (smaller than current) from back
        while index_deque and numbers[index_deque[-1]] < current_value:
            index_deque.pop()

        index_deque.append(current_index)

        # Start adding to result once we have a full window

View on GitHub (pinned to f5988cc097)

Solutions

1. Pass a positive window size (>= 1); window_size=1 returns the input unchanged
2. Clamp computed sizes: window_size = max(1, window_size)
3. Validate config before the call and raise a clear upstream error if an invalid size is configured

Example fix

# before
result = sliding_window_maximum(nums, len(nums) - k)  # k >= len(nums) -> 0 or negative

# after
result = sliding_window_maximum(nums, max(1, len(nums) - k))

def valid_window_size(window_size) -> bool:
    return isinstance(window_size, int) and window_size >= 1

When it happens

Trigger: Calling sliding_window_maximum([1,2,3], 0), sliding_window_maximum([1,2,3], -2), or passing a window size computed from an expression that can reach 0.

Common situations: Window size derived from user configuration or from a formula like len(numbers) - k that can hit zero or below on short inputs.

Related errors

• Invalid value for min_val or max_val (min_value < max_value)
• argument value for lower and higher must be(lower > higher)
• guess value must be within the range of lower and higher val
• Impossible fluid density
• Impossible object volume

AI-assisted analysis of TheAlgorithms/Python@f5988cc097 (2026-08-14). Data as JSON: /api/errors/33cd3c4f199c0aa3. Report an issue: GitHub.