Leetcode 2266. Count Number of Texts

Given a string of pressed keys (digits 2–9), count how many original letter messages could produce it, where consecutive identical digits can be grouped into letters requiring 1–3 presses (or 1–4 presses for keys 7 and 9). Compute the total number of valid partitions modulo 1e9+7 (typical solution: DP over runs with per-key max group length, n up to 1e5).