Relative Signal Echoes

In digital signal processing, an 'echo' is a sequence of values that follows the same relative progression as another. Two sequences [a, b, c] and [x, y, z] are echoes if (b-a) == (y-x) and (c-b) == (z-y). Given a stream of N integers and a pattern length K, find the frequency of the most common relative progression. Input Format: - Line 1: N and K. - Line 2: N space-separated integers. Output Format: - An integer representing the maximum frequency of any relative progression. Example: Input: 6 3 1 2 4 10 11 13 Output: 2 (Explanation: [1,2,4] -> diffs (1,2). [10,11,13] -> diffs (1,2). Count is 2.)