Count Subarrays Whose Step-by-Step Changes Match an Up, Flat, Down Pattern

You are given an integer array nums of length n and an array pattern of length m whose values are each -1, 0 or 1. Each pattern value describes the relationship between two neighboring numbers:

• 1: the next number is strictly greater than the current one;
• 0: the next number is equal to the current one;
• -1: the next number is strictly smaller than the current one.

The contiguous subarray of nums that starts at index i and has exactly m + 1 elements matches the pattern if, for every k from 0 to m - 1, the relationship between nums[i + k] and nums[i + k + 1] is the one described by pattern[k]. Return the number of starting indices i whose subarray matches.

Function Signature

def count_matching_subarrays(nums: list[int], pattern: list[int]) -> int:

Rules

• Only subarrays of exactly m + 1 elements are considered, one for each starting index i with 0 <= i <= n - m - 1.
• Matching subarrays may overlap; each matching starting index counts once.
• Return 0 if no subarray matches.

Constraints

• 2 <= n <= 100
• 1 <= m < n
• 1 <= nums[i] <= 10^9
• Every pattern[k] is one of -1, 0 or 1.

Examples

Example 1

Input: nums = [1, 3, 2, 4, 3, 3], pattern = [1, -1]
Output: 2

The subarrays of length 3 are [1, 3, 2] (up, then down: matches), [3, 2, 4] (down, then up), [2, 4, 3] (up, then down: matches) and [4, 3, 3] (down, then equal).

Example 2

Input: nums = [5, 5, 5, 5], pattern = [0, 0]
Output: 2

The subarrays starting at indices 0 and 1 are both [5, 5, 5]. They overlap, and each counts.

Example 3

Input: nums = [4, 3, 2, 1], pattern = [1]
Output: 0

Every neighboring pair decreases, so no subarray of length 2 rises.